（）镜片的尖边弧度与镜片后表面弧度一致。
A、平光
B、双凹
C、近视凹
D、远视凹
参考答案：D
因式分
（1）x2-2xy+y2
（2）x2-y2．
The USA and some other countries helped the rebels in Libya ____________ their promise to support democracy (民主) and fair trade.
A．in danger of
B．in memory of
C．in peace for
D．in return for
