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难度系数:

1.

放映幻灯时,幻灯片与镜头间距离u跟镜头焦距f的关系是(     )


A:

u < f

B:

u = 2f

C:

u > 2f

D:

 f < u < 2f

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  • 提示2PHA+5oqV5b2x5Luq5oiQ5YOP54mp6Led5bqU6K+l5Zyo5LiA5YCN54Sm6Led5LiO5LqM5YCN54Sm6Led5LmL6Ze077yM5Y2zIGYgJmx0OyB1ICZsdDsgMmY8L3A+