A lens of focal length f is placed in between an object and screen at a distance D. The lens forms two real images of object on the screen for two of its different positions, a distance x apart. The two real images have magnifications m1 and m2 respectively (m1>m2). Choose the correct statement(s).
a. m1m2=−1
b. m1m2=1
c. f=4DD2−x2
d. D≥4f