[单选题]
A microscope has an o 8s-0qrye3,of ecdt09hef y -k(od(b k3kea,abjective lens of focal length u ji 2vrir5j621.4 mm and an eyepiece of focal length 20 mm, ar 22ir6v5 jijudjusted for minimum eyestrain. A blood sample is placed 1.5 mm from the objective. How far apart are the lenses?
A. $20 \; mm$
B. $21 \; mm$
C. $23 \; mm$
D. $41 \; mm$
Post time 2024-1-26 22:03:25