Country life provides him with peace and quietness, ______ what he can't enjoy living in cities. [ ]

A. that is        

B. which is      

C. what          

D. is for which

候潮过浅水区，计划通过的最佳时间为（）。

A.高潮时

B.平潮时

C.高潮后1小时

D.高潮前1小时