短文填空

     Air is very important to everything that lives. But the air we breathe is getting (1)d______. People all

over the world are looking for ways to make it (2)c______ again.

     Have you ever watched the (3)s______ from chimneys (烟囱) rising high in the air? Have you (4)

s______ the smoke from cars and trucks on roads or the smoke from planes? The smoke is not (5)

g______ to breathe. If we want to keep fit and strong, we need to (6)b______ clean air.

     With more and more (7)f______ everywhere and more and more cars, trucks and planes, it is getting more and more (8)d______ to do with the air pollution.

     Scientists have already found (9)w______ to stop or slow down some of the things that make the air

dirty. They will not stop working (10)u______ we have clean air again.

哪些有关剪接位点的叙述是正确的？（）

A．剪接位点含有长的保守序列 

B．5′与3′剪接位点是互补的 

C．几乎所有的剪接位点都遵从GT-AG规律 

D．剪接位点被保留在成熟的mRNA中 

E．内含子3′与5′剪接位点间的距离可以很大 

F．一个内含子的5’剪接位点只能与同一个内含子的3’剪接位点作用，杂合内含子不能被剪接