Answer:
A. It was a bright and summer day. We were all hot and sticky
Step-by-step explanation:
A is the only one that makes grammatical sense. The original sentence contains a comma splice, and A helps to fix that. In B, "All of us hot and sticky" does not make any sense as it is missing a verb (were). C is missin a preposition (on). D has a sentence fragment. Through process of elimination, we can see that the answer is A.