[单选题]
A student constructs an astronomica7pqyvr *1 zvp:l telescope with a magnification of 10. If r*-*5bh( v dleq exo 6h7uq-vbthe telescope has a converging lens of focal length 50 cm, what is the focal length of the eyep hedxru-6v7o*b5*bqq hl -(veiece?
A. $2.5 \; cm$
B. $5.0 \; cm$
C. $10 \; cm$
D. $25 \; cm$
