[单选题]
A student constructs ad1x0 .p *ztz8ajbpbmr/lz b(, p1 (eir(f azbcz k,t,8n astronomical telescope with a magnification of 10. If the telescope has a con(z1 kz,ita( e fc8p,brverging 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. $25 \; cm$