[单选题]
How far from a 50-mm focal leny:2 gj)do js,3hv gs6xgth lens, such as is useq t8:;v yo-nu o )uov2rk(u9ugd in many 35-mm cameras, must an object be positioned if it is to form a real image magnified in size by a factor-;ry ouov8q(u u:t9o n2ukvg) of three?
A. $46 \; mm$
B. $52 \; mm$
C. $58 \; mm$
D. $67 \; mm$
