砌砖墙时，洞口侧边离交接处的墙面不应小于（）mm。
A．400
B．500
C．600
D．700
参考答案：B
试述肾髓质渗透压梯度形成的原理？
After you have used the materials, please put them back ________they belong. [ ]
A. where
B. to which
C. what
D. that
