辨别维生素D缺乏性佝偻病的轻重主要根据()
A.症状
B.骨骼改变
C.血钙
D.血磷
E.血碱性磷酸酶
参考答案:B
冬天我们常常用电暖器取暖,当插上电热取暖器插头后,往往会发现室内电灯变暗,为了研究这一现象发生的原因,某同学利用所学知识进行了测量。他用电压表测量标有“220 V 40 W”字样的白炽灯泡两端的电压,结果是:不接取暖器时灯泡两端的电压为210 V(如图甲所示);接电热取暖器后,电压降为200 V(如图乙所示)。假设供电局供给用户的电压U=220 V不变,不考虑灯泡电阻的变化。
(1)供电电路导线的电阻r为多少?
(2)取暖器消耗的功率为多少?
-Why didn't Mr. Smith give you one of his newlypublished books?
-I didn't want one, but he would have given me one if I ________. [ ]
A. did
B. would
C. will
D. had