Answer:
a. He committed more and more troops to Vietnam as time went on.
Step-by-step explanation:
President Lyndon Johnson first entered into the territory of Vietnam after it seemed like the Vietnam government is on the brink of collapse. President Johnson procured a law, the Gulf of Tonkin Resolution, which allowed him to use military force in Vietnam without the need to actually declare war.
The term "military escalation" means that the presence and use of military power or force escalated, increased. President Johnson did this through his authorization to send more and more troops to Vietnam.
Thus, the correct answer is option a.