[单选题]
A double convex (convex-cjgoc 2irp)8,ud4fa fxrdctnc6g+.1 1 onvexp3 h5 p2fvdibzholj v/+9vzc759n l :y) thin lens has radii of curvature 46 cm, and is made of glass of index of refraction n =p:ldv/i v55 j+9h7b9voz3plfc nh y2z 1.60. What is the focal length?
A. infinite
B. $38 \; cm$
C. $30 \; cm$
D. $18 \; cm$
