[单选题]
A plano-convex lens is s rw)o/r s x/06cn0wsltlpkbqkx (-t 38o have a focal length of 40 cm. It is made of glass of index of refr83tbl(k xkp q-action 1.65. What radius of curvature is required?
A. $13 \; cm$
B. $26 \; cm$
C. $32 \; cm$
D. $36 \; cm$
