[单选题]
A concave spherical mirror hasued3j cf-sk.: gk:mt9 a focal length o; j:6rpp/t(r4hwjhy sf 20 cm. An object is placed 10 cm ;6sy(thwj j :4r/ rpphin front of the mirror on the mirror's axis. Where is the image located?
A. 20 cm behind the mirror
B. 20 cm in front of the mirror
C. 6.7 cm behind the mirror
D. 6.7 cm in front of the mirror