[单选题]
How far from a 50-mm focal lengn/9fuu eugu6:* ;b +p ryxv2vcth lens, such as l:7 xuo 2*ke.ugi3zk) cnw-syis used in many 35-mm cameras, must an objectuuw c7 so: ie*n -.gy3z2xl)kk be positioned if it is to form a real image magnified in size by a factor of three?
A. $46 \; mm$
B. $52 \; mm$
C. $58 \; mm$
D. $67 \; mm$
