________, they have been struggling against the snowstorm for ten hours.[ ]

A. Up to now

B. By the time

C. From then on

D. In the future

下列叙述中，属于氧气化学性质的是（　　）

A．无色无气味

B．常温下为气态

C．能支持燃烧

D．液氧为淡蓝色