柴油机气门间隙应在气门处于（）状态时进行调整。
A、打开
B、关闭
C、气门重叠
D、任意
参考答案：B
平静呼吸时，非弹性阻力的主要成分是气道阻力。
_________ many times, but he still couldn’t understand it.
A．Having been told
B．Though he had been told
C．He was told
D．Having told
