Translation:It is hot in the summer.
When given a "choose one, to fill in the blank", both さむい And あつい make gramatical sense, (and is that not what this type of question is testing?), yet my curious mind gets a sour "wrong!" for expressing the grammatically acceptable なつはさむいです. There are places in the world where this is perfectly true.
antarctica i guess? They are trying to say summers = hot or warmer than normal, even antartica has a summer so to speak
なつはさむいです。That would also make sense too. It is cold in the summer.
I believe "summers are hot" is an appropriate answer here, the english translation is... far more wordy and doesn't actually reflect the sentence at all. The english translation is correct for the sentences 夏に熱いです and 夏で熱いです
That's the same, should be accepted. Both sentences have "in" in it