[单选题]
A microscope has an objective lens of focal length 1.4 -m./-yt lw/7tezivb zmm and an eyao:lk*sb d x*3epiece of focal length 20 mm, adjusted for minimum eyestrain. A blood sample is placed 1.5 mm from the objective. How far apart are the l*odl xas:b 3*kenses?
A. $20 \; mm$
B. $21 \; mm$
C. $23 \; mm$
D. $41 \; mm$
Post time 2024-1-26 22:03:25