[单选题]
An object is 15 mm in front of a convergium4d eviz 9t5f* +dq:mng lens, and mh-gce-a+z43 g kj2id the image is 4.0 mm behind the lens. Whaeadc-hz2gjg mk3 4+i-t is the focal length of the lens?
A. $11 \; mm$
B. $5.5 \; mm$
C. $3.8 \; mm$
D. $3.2 \; mm$
