--- Mum, where are my socks?

--- Under your bed. You should          your things.

A. put on            B. put down       C. put away

锅炉在开始排污时，首先要（）一次阀，然后再慢慢打开二次阀进行排污，在结束排污时，先把二次阀关闭，随后再（）一次阀。