调整气门横梁无需拆掉摇臂和凸轮轴，所有气门必须完全（）。
A.开启
B.封闭
C.半开启
D.关闭
参考答案：B
The doctor ______ and found there was something wrong with his eyes. [ ]
A. looked him after
B. checked him over
C. checked him about
手机上网安心宝的资费为（）
A.月费1元/月
B.月费3元/月
C.上网通信费可按0.01元/KB计费
D.上网通信费可按0.001元/KB计费
