[单选题]
How far from a 50-mm focal length lens, such as is used in manpz/fm3i d ynvl w59( nl((i5kty 35-mm cam t *j6gy l8o1j:imos +o q9.v3pekkz.weras, must an object be positioned if it q + w8 vks.j*z m3g.ot y9p:e1lkoj6oiis to form a real image magnified in size by a factor of three?
A. $46 \; mm$
B. $52 \; mm$
C. $58 \; mm$
D. $67 \; mm$
