[单选题]
A student constructs ja-x0u i37dk kan astronomical telesct0pb;neb6f*; v3debc ope with a magnification of 10. If the telescope has a converging lens of focal length 50 cm, what is the focal len*bvtb ;bcnpdf6e;e0 3 gth of the eyepiece?
A. $2.5 \; cm$
B. $5.0 \; cm$
C. $10 \; cm$
D. $25 \; cm$
