a 3m+1可写成 [ ]
A. (a3)m+1
B. (am)3+1
C. a·a3m
D. (am)2m+1
答案：C
Hurry! The plane ______ . You know, it ______at 3:15.
A．takes off, takes off
B．is taking off, takes off
C．takes off, is taking off
D．is taking off, is taking off
某钢厂去年产钢740万吨，消耗润滑油7232吨，今年计划产钢850万吨，要求采取降耗代用等措施使吨钢消耗润滑油比去年降低2%，求今年润滑油需用量。（提示：润滑油消耗与钢产量成正比。）
