[单选题]
A compound microscope has a 18-cm barre,:qtyn:gmr 0d l apx u3 m iw1u6j,a2i6q8kcywfd:v ::pknd an objective with a focal length of 8.0 mm. Wha :1fj :6v6u3u p2qd i:mxk8a ,ipwwkcyt is the focal length of the eyepiece to give a total magnification of 240?
A. $0.13 \; cm$
B. $1.5 \; cm$
C. $1.9 \; cm$
D. $2.3 \; cm$
