O2和CO2进出细胞膜是通过
A.单纯扩散
B.易化扩散
C.主动转运
D.入胞作用
E.出胞作用
参考答案:A
It is far better for one to drink milk,________one gets nutrients, than to drink coffee,________contains no nutrients at all.
A.what; what
B.where; as
C.from which; which
D.in which; what
从经济学的角度来看,人的欲望具有单一性和有限性的特征。