磷在钢中也是有害元素，它在钢中主要以（）形式存在。
A、FeP
B、Fe2P
C、Fe3P
D、Fe4P
参考答案：B, C
Although they had made careful preparation, unexpected difficulties________in the course of their
experiments.[ ]
A．rose
B．raised
C．lifted
D．arose
