[单选题]
A person's face is 30 cm in front of a cont*c y)g,1ill3qebe(p c3m02wc 2c x8escvnzo2 ave shaving mirror. If the image is an erect image 1.5 timesm vnc3s22zo c e02cx8w as large as the object, what is the mirror's focal length?
A. $20 \; cm$
B. $50 \; cm$
C. $70 \; cm$
D. $90 \; cm$
