车钩复原装置有哪几种?有何用途?
参考答案:
车钩复原装置有鞍式和摆式两种。其用途是使车钩在左右移动失去外力后,迅速自动恢复正位。
基因组或染色体DNA克隆
Now the air in our city is ______ than it used to be. Something must be done to stop it.
A.good
B.bad
C.worse
D.better