Time is of no importance to great thoughts, ________ are as fresh today as when they first passed through their authors' minds, ages ago.

A．what

B．that

C．which

D．where

局部通风机及其开关附近（）米以内风流中瓦斯浓度小于0.5％时，才能起动。

A、10

B、20

C、30

D、40