in which 中的which指什么?
问题描述：
in which 中的which指什么?
a pump had come into use in which expanding steam raised a piston in a cylinder,and atmospheric pressure brought it down again when the steam condensed inside the cylinder to form a vacuum.
答
which应该指a pump,
这句话的意思是：有种泵被投入使用,在它内部,膨胀的蒸汽把气缸里的活塞推起来,然后当蒸汽在气缸里凝结成水的时候会形成真空,这样外部的气压会把活塞压回去.