When the Red Cross started blood banks ______ .
A. white Americans would not give their blood
B. black Americans were unwilling to give their blood
C. no one was able to give his blood
D. both the white and the black gave blood
查看答案
收益递减规律对于一宗土地来说,表现在当对该宗土地的使用强度超过一定的限度后,土地收益开始下降。()
A. 正确
B. 错误