laos and cambodia were drawn into the fighting in vietnam
when south vietnam fell to the communists
by communists in those countries
by the khmer rouge
when the united states withdrew from vietnam

C. by the Khmer Rouge

Explanation:

Pathet Lao was a communist Laotian group by jowl with the Vietnam Congress. In the past, they have even fought a war in Laos and established government while the Vietnam War was going on. This group was a communist political movement. It was an organization that was formed in the mid-20th century in Laos. But the group gained power and assumed political powers only after in 1975, after the famous Laotian Civil War.

answer is  

loa ≅ lma

to prove that the triangles are congruent using the aas congruence