20. Last Sunday when Mr Wang was leaving Beijingfor Canada, a number of his friend ______ at the airport.

A. found him out

B. put him up

C. knocked him down

D. saw him off

词义解析：

A. found him out发现他

B. put him up为他提供食宿（更多含义：推荐）

C. knocked him down击倒他

D. saw himoff为他送行

解析：考察对动词词组含义的理解，注意平时词组的积累，根据句子含义，关键词airport机场，可得出答案D。

参考译文：上周日王先生将从北京出发到加拿大，他的许多朋友在机场为他送行。