高三英语单项选择1000题
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.