16. Whenever we hear of a natural disaster, even in a distant part of the world,
we feel sympathy for the people having affected.
解析： 人被（灾难）所影响，应该用被动语态，应改为: having been affected.
17. Mary said her mother would buy her a five-speeds racing bicycle for her sixteenth
a b c d
18. I have lost so much weight recently so all my clothes are too big; I must have
a b c
them taken in.
19. Even though he had been studying English for three years before he came to a b c
England, it is still difficult for him to make himself understand.
解析： 尽管他在去英国之前已经学了三年的英语了，但要别人明白他依然是有困难的。这里他是被人听懂，理解的，所以要用被动语态，故D项改为： understood.
20. His paper contains less mistakes than ours.
a b c d
解析： B项改为：fewer; 因为less修饰不可数名词, 而修饰可数名词应该用：fewer, 用比较级，因为后面用than, 有比较对象.