Here are the best answers for each question:

1. She said that is was **A. the** last house on the road.
2. He refused **B. to comment** after the trial.
3. A recent study of 2000 species of plants and animals **B. have** suggested an answer to this question. (The correct choice should actually be "A. Study" if we consider grammatical agreement; it should be "has" instead of "have.")

So, the refined options are:
1. A
2. B
3. A (but note that the sentence as given has a grammatical error).