[单选题]
A concave spherical mirror has a foodqe )q n5*eg1cyk dv(*:ky7tsal length of 20 cm. An object is placed 30 cm in front of the mirror on the mirror's axis. Where is the imagevky*y: 7kt sd( 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
