22．_____trying to persuade his father to give up smoking, his letter was rejected.

A．Aiming at

B．Aimed at

C．Being aimed at

D．to aim at

铺设塑料管道应符合（）规定。

A.塑料管之间的连接采用承插式粘接、承插弹性密封圈连接和机械压紧管件连接

B.各塑料管的接口应错开

C.放平，密封

D.栅格塑料管群应间隔米左右用专业扎带捆绑一次