"Il boit un café et de l'eau."
Translation:He drinks a coffee and water.
I think it's pretty rare in English to say "a coffee" rather than just "coffee".
The point of this exercise is to show the difference between countable and uncountable things. In French and in English it is possible (and in some places quite common) to shorten "a cup of coffee" to "a coffee" / "un café". He is drinking a coffee. (one cup) Il boit un café. Water, on the other hand, is never shortened to "une eau" in French. It is uncountable.
This nuance is lost if it is written, "il boit du café et de l'eau / he drinks coffee and water". How much coffee? We don't know. The meaning is different.
"He is drinking a coffee and water" Is this wrong grammatically? I am sure the app usually accepts this.
In the U.S. one would rarely if ever say "a coffee." It is coffee or some coffee, or a cup of coffee. However, I know "a coffee" is standard in Ireland. Possibly in the British Isles as well. I do not know about other English speaking countries such as Australia, Canada, New Zealand, etc. So Duo should probably accept "Do you want 'coffee,' or 'a coffee,' or 'some coffee.'"
I hear my co-workers (in the U.S.) say all the time that they are going to get "a coffee" at the Starbucks downstairs, inviting their fellow coffee enthusiasts to join them. They do not say "a coffee" in relation to coffee from the break room. That would be "some coffee" or just "coffee."
I believe that paying $5 for a cup of coffee gives it special status as "a coffee." :)
I agree that all three should be accepted.
(I don't drink coffee, no matter how it is referred to.)
I'm sure Mary-Beth always did when asking Christine if she wanted one on 'Cagney and Lacey'.
Geographically speaking Ireland (both Northern & the Republic) are in the British Isles. In British English it is the norm to say "a coffee".
It should accept "a cup of coffee" even if it is not the only way to say it, it is quite common, at least in the US.
It's a matter of conjugation.
je bois → I drink
tu bois → you drink
il/elle/on boit → he/she drinks
"Je bois l'eau" would be
"I am drinking the water"
While "je bois de l'eau" would be
"I am drinking [a general amount of] water"
"I drink water [in general]"