把一个长方形木框拉成一个平行四边形，它的周长[ ]
A．扩大
B．缩小
C．不变
答案：C
We must note that many people ____ the knowledge of first aid. [ ]
A. lack
B. lack of
C. lacking
D. are lacking
我国城市居住区绿化要求在（）以上。
A、25%
B、30%
C、35%
D、40%
