[单选题]
A student constructs ancu 6g2 ybr.wt- as uq qjfmc3+6af8ny5k (*0m wkwtronomical telescope with a magnification of 10. If the telescn +kuw86ymwf5cajmqk* 3 0(fqope has a converging lens of focal length 50 cm, what is the focal length of the eyepiece?
A. $2.5 \; cm$
B. $5.0 \; cm$
C. $10 \; cm$
D. $25 \; cm$
