（）是变压器磁路的主体部分。
参考答案：铁心
We were all surprised when he made it clear that he ____ office soon.[ ]
A. leaves
B. would leave
C. will leave
D. had left
电路如图所示，二极管为同一型号的理想元件，电阻R=4k，电位uA=1V，uB=3V，则电位uF等于（）。
A.1V
B.3V
C.12V
