当旋转机械的转动轴出现轴相微小偏移时，由探头发射的等幅射频信号包络线变成为（）。
A.原直线
B.新的直线
C.矩形波曲线
D.正弦波曲线
参考答案：B
(8分）已知有以下的物质相互转化关系，A是常见的金属单质，能被磁铁吸引。
(1)试回答： 写出B的化学式 H的化学式 。
⑵ 写出由E转变成F的化学方程式 。
⑶向G溶液加入A的有关离子反应方程式 ____。
An investigation that is unguided can occasionally yield new facts, even notable ones, and the typical appearance of such facts is the result of a search in a definite direction.
A. but the typical appearance of such factsB. but typically the appearance of such factsC. and typically the appearance of facts as suchD. and the typical appearance of facts as such
