一瓶矿泉水喝去半瓶，则剩下的半瓶矿泉水[ ]

A．质量减半，密度减半

B．质量减半，密度不变

C．体积减半，密度也减半

D．质量、体积、密度均减半

22．The site is fairly near the city center, ___ it can only be reached by a series of narrow streets．

A．and

B．but

C．or

D．So