看到三星笔试的十二套模拟卷（紫色的书）里，有几道题前后的答案真蛮搞脑子的，想请教：
模拟卷5--51题：
Our new office building will be ____________
A. fourteen-stories high B. fourteen story high
C. fourteen stories high D.fourteen-story-high
答案是C，为什么不能是D呢？
模拟卷12--39题：
The Whites have a ________baby
A. five-month-old B. five-months-old C.five month old D. five months old
答案是A。为什么不能是D呢？
又如，卷4-62：
My son loves to watch planes______at the airport.
A. taking on B. to taking on C. taking off D. to take off
答案是C
卷11里 watch sb. do sth 出现了两次
45题：The boy seemed interested in watching the old man _____repair
A. to repair B. repaired C. in repairing D. repair
答案是D
64题：My grandmother know Emma very well. She has watched her _____up
A. was growing B. grew C. to grow D. grow
答案是D
这样说来watch sb. do sth 和 watch sb. doing sth都是可以的？可是怎么区分这几种情况呢？虽然最后发现题目的选项还是可以用排除法。
感叹一声这些题目真搞脑子啊。
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