As someone else commented:
"comprehend" is a transitive verb which means it requires a direct object and this particular sentence does not have one, so you must use "understand" which can be transitive or intransitive which means it doesn't have to have a direct object.
"Entender" is more "understand" and "comprender" is "comprehend." I read elsewhere on here from a native Spanish speaker that it can be understood to be slightly ruder to say "No comprendo" because it is sort of like saying "I can't even comprehend you." It could be interpreted to shift the blame onto the speaker rather than your fault for not understanding. They went on to say that "No comprendo" is perfectly polite if there is a loud noise or somebody else was talking.
That said, if they understand you are just learning, I doubt anybody would take offense to the subtle distinction.
Except that "comprehend" requires a direct object as it is only used as a transitive verb.
Both entender and comprender can be intransitive as well as transitive like "to understand" and unlike "to comprehend" So this particular sentence cannot use "comprehend." There are some uses of "to understand" that can only be translated by "entender".
Seriously, "comprehend" should also be accepted for "comprendo", but not in this sentence because "comprehend" is a transitive verb which means it requires a direct object and this particular sentence does not have one, so you must use "understand" which can be transitive or intransitive which means it doesn't have to have a direct object.
Different forms of the exercise come to the same sentence discussion. “Comprehend” is also wrong for the translate from Spanish to English exercise as it requires a direct object, so we would use “understand” which can be used without a direct object as well as with one.
When I start googling for answers, it just raises more questions. Years ago I learned Spanish in Mexico and no one used "comprender" in conversations. I found an article from a Mexican author, José del Val, entitled, "Entender y comprender al otro" about cultural differences. I can make an educated guess how the words differ, but it would just add to the confusion.
There is more than one way to pronounce y depending on region. https://www.thoughtco.com/varieties-of-spanish-3078185
Duolingo only allows a typo if it does not make another word. A verb conjugation must have the correct ending.
If you put the wrong last letter, then it is not just a spelling error. It would be wrong. How else can Duolingo know if you know which ending is the right conjugation for “yo” ?
A spelling error that does not change the conjugation of the verb and does not make a new word will be accepted as a typo.
I think you meant entiendo? https://dictionary.reverso.net/spanish-english/Entiendo
There is a difference in use though. “Comprehend” is a transitive verb in English according to Merriam Webster dictionary which means that there must be a direct object, while “understand” can be used as a transitive verb and also as an intransitive verb as it is used here. You must say what you comprehend, but you can just say “I understand.” if you wish.
In Spanish both verbs, “entender” and “comprender” can be used as either transitive or intransitive verbs.
It uses an object in British English also: https://en.oxforddictionaries.com/definition/comprehend
Someone has since found a dictionary that lists that comprehend is intransitive as well as transitive, so try reporting it for that use in your area.
In English “to give” has both a transitive and intransitive use. So, just because a verb is transitive does not mean that it cannot be intransitive also. Scroll down past the transitive uses for the intransitive uses. https://www.merriam-webster.com/dictionary/give
However, since “to understand” is used both ways that may be why “comprehend” did not develop that second intransitive use. I suppose that you think the dictionary is wrong? https://www.merriam-webster.com/dictionary/comprehend
All of you insisting that English speakers are not allowed to say, "I comprehend," are wrong on two counts. First, even though "comprehend" is a transitive verb, in the sentence, "I comprehend," the object, "you," (or it, or the question, etc.) is implied. Second, the use of "comprehend" without an explicit object had become so commonplace as to render the issue of transitive/insensitive moot.
Show me a dictionary that agrees with you, please. People generally say "I understand." for that, while "comprehend" in English is used for more complicated information. If "I comprehend" has become commonplace in your area, please specify where and report it to Duolingo.
The OxfordLearners Dictionary shows 'comprehend' as both transitive and intransitive. https://www.oxfordlearnersdictionaries.com/definition/english/comprehend
WilliamEPo, I think you are missing the point. Nobody has said that the meaning is essentially different in any way. What they are saying, if I am not mistaken, is that if you want to say "I understand," then you MUST say "Entiendo" because "entender" does not require a direct object.
However, if you have some pressing need to use "comprender," then it requires a direct object, as in "Comprendo el arte moderno."
Sorry, it is the other way around. The two Spanish words may be used with or without a direct object. It is the English word “comprehend” that requires a direct object, according to the dictionary. The word “understand” can be used with or without a direct object. https://www.merriam-webster.com/dictionary/comprehend
The English word “comprehend” is transitive and requires a direct object. https://en.oxforddictionaries.com/definition/comprehend
The word “understand” can be used transitively or intransitively, with or without an object.
“Comprehend” is not correct here, because it is a transitive verb which requires a direct object. It means “to grasp the nature, significance or meaning of....” https://www.merriam-webster.com/dictionary/comprehend