These natural parks are very important for preserving many animals, which would ______ run the risk of becoming extinct(灭绝的)．

A．otherwise

B．other than

C．therefore

D．in another way

选择诱导油流的方法，需要遵循基本原则有（）。

A.应缓慢而均匀地降低井底压力

B.用密度小的液体将井内密度大的液体替出

C.能建立足够大的井底压差

D.能举出井底和井底周围的脏物

E.沟通地层和井筒，产生流体流通通道