基尔霍夫定律由（）几个定律组成。
A.电压定律
B.电阻定律
C.电流定律
D.电场定律
参考答案：A, C
Mr Black be at home because she called me from England just now.
A．mustn't
B．isn't able to
C．can't
D．may not
半径是3厘米的圆，它的面积是______平方厘米．
