稳压二极管的稳定区域是指工作在工作在区域
A. 正向导通
B. 反向截止
C. 反向击穿
D. 正向击穿
When _________ files, I use both sides of the paper.
A. to print
B. prints
C. printing
D. printed
Turn _______the lights when you leave the room.
A. on
B. off
C. up
D. down
______________ beautiful pen holder!
A. What a
B. What
C. How
D. How a