一次污染物是由污染源直接排入环境空气中，其物理和化学性质未发生变化的污染物
参考答案：对
Everyone in the village is very friendly. It doesn’t matter ____you have lived there for a short or a long time.
A．why
B．how
C．whether
D．when
天然气浅冷的制冷温度不高于（）℃。
A-15
B-18
C-28
D-45
