[单选题]
How far from a 50-mm foc1 zcb8ffioz.28vz)m4 kztt ja zcy 6m9-u52cfal length lens, such as is ugc/wts/(5bphl2;qkn sed in many 35-mm cameras, must an objen;csh/k2tq(5lg / bpw ct 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. $67 \; mm$
