Question

when does gravitational lensing occur? dark matter becomes visible using certain kinds of telescope lenses. high concentrations of dark matter cause length contraction of nearby objects. a massive object (like a galaxy cluster) bends the light from an object (like a quasar) that lies behind it. the gravity from an einstein ring magnifies nearby objects.

Explanation:

Gravitational lensing occurs when a massive object's gravity bends light from a more - distant object behind it. A galaxy cluster can act as such a massive object and bend the light from a quasar behind it. Dark matter is not directly related to the basic concept of gravitational lensing in the ways described in the other options. An Einstein - ring is a result of gravitational lensing, not the cause of it in the context of the question.

Answer:

A massive object (like a galaxy cluster) bends the light from an object (like a quasar) that lies behind it.