[单选题]
A student constructs an astronxqy*txxf i3 :qn5l1m-mju:o - zm4o:l omical telescopb1bjj; iyq.f 77muo 7ie with a magnification of 10. If the telescope has a converging lens of focal length 50 cm, what is the focalbum;7f .i7 17o jyqjbi length of the eyepiece?
A. $2.5 \; cm$
B. $5.0 \; cm$
C. $10 \; cm$
D. $25 \; cm$
