题目

What did the boy's mother use to be like? A . She was thin. B . She was tall. C . She had long hair. 答案：C关于电动势，下列说法正确的是（ ）A. 电源两极间的电压等于电源电动势B. 电动势越大的电源，将其他形式的能转化为电能的本领越大C. 电源电动势与外电路的组成有关D. 电动势的数值等于内外电压之和