从 A, B, C, D四个选项中,选出可以填入空白处的最佳答案:
1. – Jack?
-- ____.
A. Present, Sir. B. I am, Sir C. Here, Sir D. Yes, Sir.
2. ---What are you busy with ?
--- We are carrying out a research ____ the causes of cancer.
A. into B. onto C. to D. in
3. ---____ the paper ?
--- No, I have still got one page to finish.
A. Have you done B. Do you do C. Did you do D. Had y