墙下条形基础的素混凝土垫层强度通常为（）。
A.C10
B.C15
C.C20
D.C25
参考答案：C
The koala sleeps ______, but gets up ______. [ ]
A. during the day; at the evening
B. at day; during night
C. in the day; during the evening
D. during the day; at night
把一串点知觉为一条虚线反映了知觉的( )。
A．整体性B．理解性C．选择性D．恒常性
