[单选题]
A student constructs an ast bl12 rq+wwh9/ n:96ut/xw jn/scjtdtronomic hu8kyh )ai)b2al telescope with a magnification of 10. If t2hya 8uh )k)ibhe telescope 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. $25 \; cm$
