[单选题]
When a person stands 40rnx*z4 4rzjw e8c3 j1o cm in front of a cosmetic mirror (concave mirroytid5e(wa/r drf gk/86wnf 7*6bj s8 wr), the erect image is twice the size of the object. * rkwew f76w6 b5sdjrfyi g/ntd(a/88 What is the focal length of the mirror?
A. $27 \; cm$
B. $40 \; cm$
C. $80 \; cm$
D. $160 \; cm$
