人工煤气分为()
A.5R
B.6R
C.7R
D.8R
参考答案:A, B, C
— Would you do me a favor to choose a wedding dress?
— Of course, but it is a matter of personal _____.[ ]
A. concern
B. sense
C. style
D. taste
产品缺陷是产品责任中最为关键的要素。