B) The United States pulled out and the North Vietnamese eventually took the entire country
Nixon pulled out troops in 1973 under his Peace with Honor plan. Special forces were left behind to help South Vietnam but ground troops were removed.
With the Vietnam War losing support more and more during Nixon's presidency, he decided to remove ground troops in 1973. Special forces remained to help train South Vietnamese troops and the US continued to support the South financially. Despite, the remaining help the North continued to invade the South. South Vietnam surrender and fell to the North in 1975. The country was reunited under a communist government.