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Formula of magnification of astronomical telescope is
Difficulty: Easy
A: 
$\rm{\frac{f_{e}}{f_{o}}}$
B: 
$\rm{\frac{d}{f_{e}} +1}$
C: 
$\rm{\frac{f_{o}}{f_{e}}}$
D: 
$\rm{\frac{d}{f_{o}} +1}$