[单选题]
A student constructs an a njju3xe(.-3+wipl 3 kh*fkykstronomical telescop8jt.lsqn;eae- f4c r.e with a magnification of 10. If the telescope has a converging lens of focal lenjseen8l.. ct q4 f;-ragth 50 cm, what is the focal length of the eyepiece?
A. $2.5 \; cm$
B. $5.0 \; cm$
C. $10 \; cm$
D. $25 \; cm$
