当蓄电池进行核对性充放电时，在放电完了之后应立即充电，一般情况下当放电容量达到（）时即应充电。
A.50％
B.60％
C.70％
参考答案：C
----Is that Tom speaking?
----Sorry, he is out now. He _______ the cinema with his classmates.
A．has been to
B．has gone to
C．have been to;
D．have gone to
现代长颈鹿长颈的形成是下列哪项的结果 [ ]
A．人工选择
B．过度繁殖
C．遗传变异
D．自然选择
