The correct option is:
B. To destroy Communist strongholds and strengthen South Vietnam.
The Cambodian Campaign a military operation carried in eastern Cambodia by the United States and the Republic of Vietnam (South Vietnam). It was during 1970, as an addition to the Vietnam War and the Cambodian Civil War. This policy by President Richard Nixon was aimed to defeat the nearly 40,000 troops of the People's Army of Vietnam (PAVN) and the Viet Cong (VC) in the eastern border of Cambodia.