儿童早期智力发展迅速，4岁时儿童智力已发展了约成人智力的（）
A.20%
B.50%
C.80%
D.92%
参考答案：B
当地基为( )时，可将地基做成台阶形。
A．易风化岩石
B．不易风化岩石
C．软质岩石
D．整体岩石
April 1st is a special day, ________ practical jokes may be played without punishment.[ ]
A. in which
B. on which
C. with which
D. for which
