Answer:
B) Schools were forced to close.
Step-by-step explanation:
The antiwar movement began in the mid-1960s and lasted until 1971 against the presence of United States troops in Vietnam.
By the year 1970, President Richard Nixon announced the expansion of the war into Cambodia. This produced an intensification of the antiwar movement, especially in the universities, high schools and college campuses. More than 450 of these were shut by students strikes who carried violent and non-violent protests. On Kent University 4 students were killed by the National Guard.
It was known as the National Student Strike and it was the only in U.S. history.
I hope this answer helps you.