Gravitational Lensing Is Caused by the Bending of Light as It

Gravitational lensing is caused by the bending of light as it passes a massive object. Why does gravitational lensing so often involve quasars?

A) because they are among the most massive objects known
B) because they are all so far away
C) because their radiation is narrowly confined to particular regions of the spectrum
D) because astronomers can observe most quasars up off the galactic plane where they are not obscured by gas and dust