如图所示为草原生态系统的食物网示意图，能量从蛇传递到鹰的效率约为（ ）
A．10%～20%
B．50%～60%
C．80%～90%
D．100%
答案：A
The children went home from the grammar school，their lessons ________ for the day.
A．finishing
B．finished
C．had finished
D．were finished
安全带进行静载荷实验的时间为（）min。
A.5
B.3
C.10
D.15
