压缩后的天然气必须冷却（高温气体直接注入，会在气井套管和周围水泥环引起不均衡的应变）、净化。Compressed natural gas must be cooled (high-temperature gas injected directly causes unbalanced strain in the casing and surrounding cement rings) and purified.

A.-1,0,0,0,1,1,2,0,0,1,2,3,4,5,6,0,1
B.0,1,0,0,1,1,2,0,0,1,2,3,4,5,6,0,1
C.-1,0,0,0,1,1,2,0,0,1,2,3,4,5,6,7,1
D.-1,0,0,0,1,1,2,3,0,1,2,3,4,5,6,0,1

A、0
B、1
C、1/s
D、以上都不是

A、道德层面
B、现实层面
C、感情层面
D、自我层面