Sometimes I enter the discussion to see comments and try to learn something about Vietnamese grammar. Do you see something wrong with the Vietnamese sentence here?
We do not work with a context in Duolingo, so just try to see this sentence as a part of an extended phrase or paragraph. We have practiced (the most in this course) with many English sentences before, so it is easy to add time adverbs (maybe some date, moment, or hour of the day) to use this sentence in simple present. But perhaps we cannot do the same with the Vietnamese sentence yet, then it is better to practice with short and simple sentences (or only the part of a longer sentence).
The thing is, from my understanding of Vietnamese, a phrase like the above tends to be said in a present continuous tense. Thus an "-ing" should be acceptable as much as Duolingo is accepting the present tense.
Duolingo does not give context, but the common context such phrases that Duolingo uses is something valid to discuss. Else, we don't know for sure if phrases like this one is usable when grandma is eating the apple in a continuous action or she has some habit of eating your apples from the fridge.
So just trying to read it as a clip from a paragraph without about it is not the solution. Discussing how phrases like these is used is just a important as discussing grammar.
Yes, it is absolutely important but I do not like to compare between the English and Vietnamese grammar. I have seen for example the phrase "I am the man", so that exercise is focusing in the use of Vietnamese classifier (người, for a person or people) and also a native speaker once explained that người is the noun and đàn ông means male, as an adjective. If I add này then the phrase is "I am this man", Tôi là người đàn ông này.
I think many people think this is very confusing, but it is not when you see the order of the Vietnamese sentence and stop thinking in the English structure:
first, you have the subject (in this case, just the pronoun), then it is the "verb" but I think this word là is not really a verb and sometimes it can be excluded from the sentence
next, if người is a noun, đàn ông is describing the noun as an adjective but đàn ông means man and người đàn ông also means man.
at last, này is meaning "this" and it is always after the construction người + đàn ông or only đàn ông
We can see that understanding this grammar is a very new experience. In my case, I think that knowing some basic Indonesian grammar, since near two years ago, has helped me a lot and I am still discovering a marvelous world with this more complex and tonal language. Indonesian is indeed much simpler than Vietnamese because that use the Latin alphabet without diacritics so we do not have tones, but the complexity of the grammar, the word position and multiple pronouns (formal and informal, and two pronouns for we, including or excluding the interlocutor) make it a good challenge, also with the agglutinative structure.
In the other hand, Vietnamese is not only a challenge for the use of tones, also because we need to learn to use word structures combining monosyllables in almost the whole text, but both languages share similarities about the word order in affirmative and negative sentences, also with the possessives and tense markers. If we compare the question structure I think they are very different but always keeping the similarities in the order between nouns and modifiers.
All this comparison between two Asian languages is only to show that we do not need to focus on English grammar when learning Vietnamese. We just need to discover something very very new and different. I know this is more than obvious. :))