The correct answer is option D. "The U.S. wanted to defeat the communist troops who were there". Nixon authorized the invasion of Cambodia on April 28, 1970, allowing combat troops to cross the border from South Vietnam into Cambodia. The main reason why U.S. wanted to enter Cambodia was to defeat the communist troops that were residing there.
An archaeologist deals with human history. A paleontologist studies fossils. and an anthropologist studies with past and present humans