How Have Astronomers Searched for Evidence of MACHOs in the Halo

Multiple Choice

How have astronomers searched for evidence of MACHOs in the halo of the Milky Way?

A) They search for stars that are binary companions of MACHOs.
B) They search for rapidly moving massive gas clouds.
C) They search for disturbances in the background of gravitational waves.
D) They search for distant stars with light briefly amplified by gravitational lensing.
E) They search for close binary stars undergoing mass transfer.