将低频信号“加载”到高频振荡信号上去的过程称为（）。
A.调频
B.调幅
C.调相
D.调制
参考答案：D
—Where did you pick up this wallet?
—It was in the supermarket _____ I did some shopping yesterday. [ ]
A. that
B. which
C. where
D. as
高压水银荧光灯和金属卤化物灯的光通量与电压的关系为（）。
A.电压降低10%，光通量约降低27%
B.电压升高10%，光通量约升高21%
C.电压降低10%，光通量约降低21%
D.电压升高10%，光通量约升高10%
