18. We all agree that a long dress is appropriate _____ a formal wedding.

16. Experiments of this kind ____ in both the U.S. and Europe well before the Second World War.

Conversation 28. 

49.    , drink-making techniques, equipment and packaging are exhibited in the exhibition.

17. Leave your key with a neighbor ____ you lock yourself out one day.

（  ）52. In response to an economic crisis, it is advisable to take risks.

61. 真正的友谊就像健康一样，失去了才觉得宝贵。

27. I devote my whole day to ____ the English grammar.

37. Why is space junk considered a problem?

50.The organizing committee of the exhibition is   50  .

25. She was the only one of the girls in our class ____ accepted as a candidate for the president of our Students’ Union.

65. 尽管互联网技术现在已经十分先进，但是在一些发展中国家互联网在普通用户中还远远没有普及。