下列计算正确的是（ ）
A：（x2）3=x5
B：a+2a=3a2
C：（﹣mn）5÷（﹣mn）3=m2n2
D：a3•a4=a12
选举权和被选举权是人民参与管理国家和管理社会的基础和标志。
—What were they doing from 8:00 to 10:00 p.m. last night?
—They ____ (use) the Internet.
The manager is busy at the office; you'd better leave him ________.（ ）
