如图是物体S通过凸透镜成像的示意图,当物体S放在哪个位置时,才能产生图中所成的像S′
A.u>2f
B.f<u<2f
C.u=f
D.u<f
A
What's in the classroom?[ ]
A. It's a picture.
B. It's black.
C. A board, two lights, many desks and chairs.
法兰连接时,法兰盘、紧固件应经()处理,并应符合设计要求。
A、紧固
B、防腐
C、冷却
D、刮削