题目

内阻不计的交流发电机产生电动势E=10sin50πt (V)，接有负载电阻R=10Ω,现把发电机的转速提高一倍，则A.负载两端电压的有效值将变为28.2V     B.交流电的频率将变为100HzC.负载消耗的功率将变为20w            D.负载消耗的功率将变为40w 答案：C用括号中所给动词的适当形式填空。1. There’s no reason ________ (come) to school late today.2. I ________ already ________ (finish) my homework, so I can play now.3. Email English is a new kind of ________ (write)English in the modern world.4. Many man-made satellites ________ (send) up into space so far.5. It's my turn ________ (clean)the classroom.