We all know that Chinese students usually study very hard for long _____. This is very good,but it doesn't help a lot.
A.time
B.hours
这么混账的题，为什么答案是B而不能是A？

可以说for long hours，却不能说for long time.

但是可以说for a long time。

这里不能少这个冠词 a。

for long hours是“很长的时间”，中性的，纯指时间；

例：

1. Computer Science, Literature, Sitting for long hours.
电脑科学，文学系，呆坐。

2. It is also feared that if a woman works at a computer for long hours, the unborn child in her body might be killed.
而且人们耽心如果孕妇长时间使用电脑工作，她体内的胎儿可能会死去。

3. Oh yeah. I had lots of free time to eat too much. And I even got to a couple of movies and sit at the computer for long hours.
喔，是啊！我时间多到可以狂吃到撑。我还看了几场电影，还有坐在电脑前好几个小时。



for a long time是“很长的一段时间”，

例：

It hasn't rained for a long time.
好久没有下雨了。


Henry VIII reigned for a long time.
亨利八世统治了很长一段时间。

He remained tongue-tied for a long time.
他半天说不出话来。