开关电源变压器的损耗主要包括（）。
A、磁滞损耗
B、铜阻损耗
C、涡流损耗
D、介电损耗
参考答案：A, B, C
The teacher commanded that the exercises _______ in an hour.
A. was finished B . were finished C should finish D. be finished
烟流抬升高度
