[单选题]
A concave spherical mirror has a focal length of 20 cm. Ab eq-wi k t+6f*c+y d+5ov2eexn objectf;e q 4l7h jxdbn5.l-w is placed 30 cm in front of the mirror onl; qfwe7nbx-4.hl jd5 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
