When Does Gravitational Lensing Occur

When does gravitational lensing occur?

A) when light passes near a massive object and is deflected by the object's gravitational field
B) when a galaxy has a central black hole with an accretion disk
C) when the mass of a galaxy is greater than expected from the luminosity of the galaxy
D) when the mass of a galaxy is less than expected from the luminosity of the galaxy