把一个图形按3：1放大后，周长的变化是 [ ]
A．扩大3倍
B．扩大6倍
C．扩大9倍
D．周长不变
答案：A
His radio is a very old one. It sometimes works and sometimes it_______
A．seldom does
B．does hardly
C．never does
D．doesn’t
高温炼焦的化学产品的产率取决于（）。
