Each guide was helpful, but we forgot to thank them.
You should use the plural pronoun, because we don't know whether the guides were only males, or females, or whether there were both sexes.
I believe it's
B. Were swimming
I think the answer is C lol
The basic structure of an informative essay is very simple. It needs to have a beginning, middle, and end. These are known more formally as the introduction, body, and conclusion, respectively
