存放袋装水泥时,四周离墙至少要()
A、20cm
B、30cm
C、40cm
D、50cm
参考答案:B
—If you like the new house, you'd better buy it.
—But it's really expensive. I can't _____it. [ ]
A.afford
B.get
C.buy
D.spend
简述最近发展区的概念及其意义。