1# ydw1163
There are two ``have to" and two ``donnot have to'' between China and North America:
In China, Ph.D students DONNOT HAVE TO work so hard and so long;
But high school students have to work so hard and so long.
In North America, all the Ph.D students HAVE TO work so hard and so long
But high school students DONNOT have to work so hard and so long.
If you see the difference, you will see the results!!!