"He swims fast and runs slow."
What's up with Duolingo's insistence on 很 for all descriptions? In many cases, like this one, you don't need it at all! With 很 here, the translation should more likely be He swims very fast, and runs very slow.
I'm pretty sure 他游泳很快和跑步很慢 is also correct. They're forcing a grammatical construction that they haven't taught. In addition, the people saying that the word bank doesn't offer 得 enough times to get the answer right are correct. I did it twice - the first time, there was only one 得 and the second time, there was a 游得 and a 得.
Well, since 慢 and 快 are antonyms, 还 can't be used to connect those ideas. You could use it to link two qualities for example (He runs fast and (also) jumps high). If you're really looking for a linking word here, you should go for 但是，可是，不过，but the idea of opposition is not explicit in the original English sentence. In Chinese, the comma does the connecting job perfectly. Its use is different in English though, which is why it has to be translated by "and". Unfortunately, I don't have the necessary knowledge to tell you which connecting word(s) could replace the comma in the Chinese sentence, but both 和 and 还 sound definitely wrong to me.
Oh boy, time to take a dive in the grammar books.
"The complement of manner in its simple form consists of 得 followed by an adjective, usually with a degree adverb or negator." Examples follow, with degree adverbs and negators 很、非常、太、最、不、不太, and a note that says the degree adverb or negator is "almost indispensable."
Source: Yip Po-Ching and Don Rimmington (1998), Basic Chinese: A grammar and workbook, Unit 22, point D (p. 167).
BTW, this construction can only be used to describe a state of affairs, not an event, according to "The Complex Stative Construction," ch. 22 of Charles N. Li and Sandra A Thompson (1981), Mandarin Chinese: A functional reference grammar (pp 623-630).
There are more examples, including one or two more degree adverbs/negators, at
Because that is too narrow of a translation. 很 does not always mean 'very', or more specifically act as a measure of degree of intensity.
Explanations and examples here: https://www.digmandarin.com/using-hen-with-adjectives.html
It also sounds awkward to not use 很 here. If someone runs exceptionally fast you can think about using 特别快 or 非常快 and then express astonishment when they finish their run with 《这么快？！》。
I believe for similar reasons that 游 and 跑 are separated by 的 when speaking about playing sports in the past tense. The best way I can describe it is that the 'active verb' part of these compound words is the first word and therefore we're modifying that by giving it an adjective.
For example, 跑步 means something like "run（跑） steps（步）" (ie, jogging/running). We're not saying their steps are slow/fast, it's the running of the steps that's slow or fast. So we have 跑步跑得很慢 .
One thing that helps is to recognize that there is not a 1-1 exact match of English to Chinese, (for example "running" vs 《跑步》). Some of these words in Chinese are 'compound words'. Use something like Google Translate to break down Chinese words into their various parts and it will also help you infer grammar and have a better understanding of the words themselves.
Lina - no, you don't need to use that form (which, frankly, is a little clumsy for this sentence), it said have been more like 他 X 得很 adv 也 Y 的很adv. Looks like the Duolingo is half baked like a lot of them. This exercise's form isn't wrong, but unless your stressing the dichotomy, or just feel like using it, it's not what I think most speakers would choose.
Native speaker here. It's hard to explain, but it sounds unnatural if you use the two-character form of the verb before 得. The way I see it is the first character is the actual verb, and the second character is a noun/modifier. For example, in 跑步, 跑 means to run and 步 literally means step. So you attach the 得 to the "actual" verb 跑 and not the phrase 跑步.
This may be the same reason why many speakers (in my experience) prefer saying 可不可以 and 认不认识 over 可以不可以 and 认识不认识.
The video link posted by theShmuli will help a lot, but basically the "verb" here actually has 2 parts; 游 (tour/ travel) which is the verb and 泳 (swimming) which is the object. 游泳 tells us what's happening then because 游 is the action we want to describe (modify) as fast you have "游得很快". This should also help with "separable verbs" https://resources.allsetlearning.com/chinese/grammar/Separable_verb#Structure_4
Disregarding the fact that you don't need a semicolon there to begin with and a comma should suffice, I can't even produce that semicolon! My Sogou typing software can't create it. I even tried switching to a Japanese character set, and it couldn't create it either. Had to copy paste!! So frustrating.
和 is usually used for combining two subjects or nouns together and can be roughly translated as "with", like "我和我朋友会看电影" (me and my friend are going to see a movie). My teachers have told me to always just separate verb clauses with commas and avoid using 和 in that sense. Not that it is always wrong to use 和 to link verbs, just that they are special use cases that are kinda tricky: (here's a guide for linking verbs with 和 if you're interested) https://resources.allsetlearning.com/chinese/grammar/Expressing_%22and%22_with_%22he%22_(advanced)
As for using the "compliment de" to modify a compound verb, you have to repeat the first part (or "action verb") of the compound followed by the 得, and then your modifiers. So, V1 + V2 + V1 + 得 + ... . -> “跑步跑得。。。”
Sometimes this is just a lot to say or to write so I usually just use the "adverbial de", although it might have a slightly different connotation (pls some native speaker correct me). The "adverbial de" kinda acts like the "-ly" after verbs in English. “他跑步跑得很慢” -> “他很慢地跑步” The "de" is pronounced the same, but is written like 地 and follows a different structure than 得. The English translation is slightly different (so I'm told). "He runs slow" -> "He runs slowly".
Here's also a link to the basics of the structural de: https://resources.allsetlearning.com/chinese/grammar/Structural_particle_%22de%22