He started when he was young. [ ]
A. write
B. writing
C. to write
D. writes
答案:B
铝合金防水卷材是一种以铝和( )等金属合金为主体材料的防水卷材。
A.硫
B.磷
C.硅
D.锡
经济活动分析法是对比法和因素分析法。