[单选题]
A person's face is 30 cm in fgg8 . xptw6 j37gqkzb58c8mwtt kz vab(3v) x+i9j-cuz gm9c;ront of a concave shaving mirror. If the image is anacv)v 9uz;3-t +icx9(m bzjgk erect image 1.5 times as large as the object, what is the mirror's focal length?
A. $20 \; cm$
B. $50 \; cm$
C. $70 \; cm$
D. $90 \; cm$
