[单选题]
A plano-convex lens iqg ecj/( qydh -vr ughr95;mu5/2y/nvs ,nrdzk 6c95 lw.fxi t4cvi p2;to have a focal length of 40 cm. It is made of glass of indexzxk cli4vcd t5r6.fw 92;pin , of refraction 1.65. What radius of curvature is required?
A. $13 \; cm$
B. $26 \; cm$
C. $32 \; cm$
D. $36 \; cm$
