题目

下列运算正确的是（） A . a3·a2= a5 B . 2a－a＝2 C . a＋b＝ab D . (a3)2＝a9 答案：ASuccess in life doesn't happen      . It's the result of devoting your time and energy to what you've set out to do.   [     ]A. by force      B. by design     C. by accident     D. by choice