—A medical team was sent to Japan by air five hours ago.
—So they have arrived by now. The flight usually takes four hours or so.
A. might
B. could
C. must
D. need
网友回答
A. might
B. could
(答案→)C. must
D. need
解析：考察情态动词表示推测。Must have done表示对过去发生事情的肯定推测。结合句意可知本题是对过去发生事情的肯定推测。句意：—一支医疗小分队五天前飞去了日本。—那么到现在他们肯定已经到了日本了。