Question refers to the graph below. Graph showing the number of American troops in Vietnam from 1960 to 1969. The graph shows the following data: 1960 has 900 troops, 1961 has 3,205 troops, 1962 has 11,300 troops, 1963 has 16,300 troops, 1964 has 23,300 troops, 1965 has 184,300 troops, 1966 has 385,300 troops, 1967 has 485,600 troops, 1968 has 536,100 troops, and 1969 has 475,200 troops.
American War Library

Which of these contributed to the trend on this graph?

Escalation of Chinese and Soviet troop levels in Vietnam
Increasing use of air power to try to defeat the Vietcong
Unprecedented presidential control of U. S. military forces
Military reports that the U. S. was on the verge of winning the war