--Which sentence is INCORRECT? --____________.A. My parents have got married since 1992.B. They have known each other well for quite a long time.C. We haven’t heard from Jack since two weeks ago.
Louis Pasteur was a world-famous French chemist and biologist. He is particularly famous for his work on rabies vaccine (狂犬病疫苗). The rabies virus enters the body through the bite of a
试讨论x→0时，f（x）的极限. 
（ax+b）=b，
f（x）=a.
f（x）不存在；
f（x）=
f（x），此时
f（x）=a=b.