[单选题]
A student constructs an astronomical telescope 1l2w4s n6ag+au9nxb d with a magnification of 10. czzr0q00g 4w.cfka. lfaw-9p If the telescope has a converging lens of focal length 50 cm, what is the focal length of 4 0c9ka0wz.zqra . pl wffc0-gthe eyepiece?
A. $2.5 \; cm$
B. $5.0 \; cm$
C. $10 \; cm$
D. $25 \; cm$
