精制装置有几条管线与低压瓦斯系统相连？（）
A.1
B.2
C.3
C.4
参考答案：C
根据工资、薪金所得九级超额累进税率表，当全月应纳税所得额由2000元增加到2001元时，边际税率是（）。
A.10%
B.15%
C.50%
D.100%
John promised his doctor he ________ not smoke, and he has never smoked ever since. [ ]
A. might
B. should
C. could
D. would
