"We must keep the office clean"
"Have to" and "must" are both applicable?
I agree. 要 has many translations and as far as I understand, it should come out of the context which one applies. If there is no context, all of those meanings should be accepted.
"We want to keep the office clean." should be accepted.
Clearly in this lesson no one is reading the reports. There are many obvious corrections reported for about a year now.
this lesson has many many instances where the right answer is not accepted.