[单选题]
When an object is 40 m cor 8;0if h rpi)d5-biit- 6.oxxrgvvika9 zw r *d*(0in front of a converging lens the inverted image is half the size of the object. What is the focal length of tvowarx tiv* k0i9z*6x( r-g.dhis lens?
A. $13 \; cm$
B. $20 \; cm$
C. $40 \; cm$
D. $53 \; cm$
