[单选题]
A compound microscope flg3n-+yes c*.q1b q ,wa(yorhas a 18-cm barrel and an oblbv/ 5ix3j ul0jective with a focal length of 8.0 mm. What is the focalljix0l5b v/ u3 length of the eyepiece to give a total magnification of 240?
A. $0.13 \; cm$
B. $1.5 \; cm$
C. $1.9 \; cm$
D. $2.3 \; cm$
