边际土地
参考答案：
边际土地，指生产所得收人仅够支付生产费用和开垦投资利息的土地，边际土地收支相抵后，无余额支付地租.
When he saw all his books _____ here and there on the floor, he knew that something terrible _____. [ ]
A. lying; must have happened
B. lie; must happen
C. lay; might have happened
D. had lain; could have happen
简答同音词与同形词的关系。
