题干
Peter doesn't smoke now, but he ________ for almost twenty years.
A：was smoking
B：had smoked
C：has smoked
D：smoked
答案(点此获取答案解析）
D
Peter doesn't smoke now, but he ________ for almost twenty years.
A：was smoking
B：had smoked
C：has smoked
D：smoked
cC (g) + dD(g)，反应达到平衡后，将气体体积压缩到原来的一半，当再次达到平衡时，D的浓度为原平衡的1.8倍，下列叙述正确的是（ ）