II. 单项选择：
21. Experts say that Longtan hydropower project, China’s third largest, will be _________ great help to _______ flood control and improving condition for shipping.
A. 不填； the B. a; 不填 C. a; the D. the; the
22. —— I really appreciate you looking after my baby when we were away for my friend’s wedding yesterday.
—— _______________.
A. Don’t mention it. B. Please don’t be so thankful
C. With pleasure D. All right
