Question

已知平面M交平面N=直线L,a含于平面A，b含于平面B，a交l=A,b交l=B,求证，a,b是异面直线。

Answer 1

假设a,b不是异面直线
则a,l确定的平面和b,l确定的平面为同一平面，也就是M和N为同一平面。
与题意不符
由此得证

Answer 2

At present there are more than one　hundred million people suffering
from　starvation , As a member of this big family in　China ,do we have the reason
to waste ? No !So what should we do to reduce the　unnecessary waste of food in
the dining　table ? Recently, more and more people　begin to realize the
importance of saving , apopular action called “Clear your plate”encourages the
public to eat up the food intheir plates . I strongly agree with this　campaign .
Besides , many rest　aurants startto provide the guests with
half-portioned　dishes、smaller dishes and assorted dishesin order to reduce the
waste , and inspire the　customers to take left　overs home . I think　these good
phenomena indicate that we will　get great progress in food saving .