犬瘟热病毒的血清型有()
A.1个
B.2个
C.3个
D.4个
E.5个
参考答案:A
在测量小灯泡额定电功率时,电压表出现了故障不能使用,小明向老师借了一只定值电阻R0,设计了如图所示的电路,按下面的顺序测量额定电压为U额的小灯泡的额定功率(R0、U额为已知、电流表的内阻小,可忽略不计):
(1)测量时,先闭合开关S和S1,调节滑动变阻器,当电流表的示数为 时,小灯泡正常工作;
(2)断开所有开关后,保持滑片P的位置不动,再将开关S和 闭合,读出电流表的示数为I;则通过小灯泡的电流为 ;
(3)算出小灯泡的额定功率P额= (用I、U额 和R0表示)。
用所给单词的适当形式填空。
1. Peter likes matchbox covers. He has a large ____ (collect).
2. The little boy is ____ (interest) in model planes.
3. The Spring Festival is as ____ (excite) as Christmas.
4. Life is much ____ (difficult) for them than before.
5. Please help ____ (you) to some chicken, boys and girls.