[单选题]
A concave spherical mirror has a fln 6 ux8cj./kfocal length o:-zeafk *j(/ p eog3wtf 20 cm. An object is placed 30 cm in front of the mirror za (p/w:o3jge *ekft-on the mirror's axis. Where is the image located?
A. 12 cm behind the mirror
B. 12 cm in front of the mirror
C. 60 cm behind the mirror
D. 60 cm in front of the mirror
