[单选题]
A plano-convex lens is tqfkf 5d -t7*v:t/siwo o haveh a4(uh+j1has jl6hxp: :9dc i1dmhp( a focal length of 40 cm. It is made of glass of insa m i+1xah:jlpu:jhh d4( pd6hhc19(dex of refraction 1.65. What radius of curvature is required?
A. $13 \; cm$
B. $26 \; cm$
C. $32 \; cm$
D. $36 \; cm$
