佛尔哈德法的指示剂是()。
A、NH4SCN
B、AgNO3
C、NH4Fe(SO4)2 ·12H2O
D、Fe2+
参考答案:C
两个不接触的磁体间的相互作用是通过______发生的.
Many questions ________ at the meeting, but he answered none.
A.came up
B.raised
C.were talked
D.asked