child的复数形式是____.

用“who”或“that”填空
(1) The man____  is talking with my mother is my father .
(2) That book is the one____  I bought yesterday .
(3) He is one of the workers ____  been saved in that accident .
(4) They talked of the things and persons ____  they remembered in the factory .
(5) All____  can be done must be done .

两根电阻丝的电阻分别为 2 欧和 16 欧 , 将它们串联接在同一电源两端 ，则通过它们的电流之比为

动物分为脊椎动物和无脊椎动物两大类，下列属于脊椎动物的是（ ）

This apple is small. I want the b____one.