使用显微镜时,如果光线较弱,应调节的结构是[ ]
A.用较大光圈或用平面镜
B.用较大光圈或用凹面镜
C.用较小光圈或用平面镜
D.用较小光圈或用凹面镜
答案:B
—Do you like _______ to music?
—No, I _______. [ ]
A. listen, don't
B. listening, do
C. listening, can't
D. listening, don't
电器设备的电压等级按带电部分对地电压分为哪几类?