工作面支架必须垂直于煤壁，支柱打成直线，其正负偏差不超过（）mm。

A、200

B、100

C、300

_______he is, he seldom shows his precious coins to others.

A．Coin-collector as 　

B．As a coin-collector

C．A coin-collector as

D．Coin-collector that