关于滤过机理的叙述正确的是

A．筛析作用指固体粒子由于粒径大于滤材的孔径而被截留

B．砂滤棒、垂熔玻璃漏斗滤过属于筛析作用

C．深层截留作用是指粒径小于滤过介质孔径的固体粒子进入到介质的深层被截留

D．微孔滤膜和超滤膜滤过属于深层截留作用

E．滤饼滤过的拦截作用主要由所沉积的滤饼起作用

Before agriculture ________, people made their living by hunting wild animals and their life was _______ of

nature.

[      ]

A. came into being; at the mercy

B. was born; in the mercy

C. began to exist; in danger

D. appeared; with the mercy