∑IR＝∑E适用于（）。
A.复杂电路
B.简单电路
C.有电源的回路
D.任何闭合回路
参考答案：D
The girl spends at least as much time singing as she __________.
A．studies
B．does studying
C．is studying
D．does to study
主井兼作进风井应采取哪些措施？
