Where was the tactic of the sit-in protest first used?

AAt a Woolworth's lunch counter in Greensboro, North Carolina
BAt a high school in Little Rock, Arkansas
COn a bus in Birmingham, Alabama
DOn a march in Selma, Alabama

Verified Answer :

The tactic of the sit-in protest was first used "c. On a bus in Birmingham, Alabama," since this led to the official "bus boycott," in which blacks refused to ride busses and give money to the state. 

Answer:

a. At a Woolworth's lunch counter in Greensboro, North Carolina

Explanation:

Later, the sit-in was adopted as a major tactic in the civil-rights struggle of American blacks; the first prominent sit-in occurred at a Greensboro (North Carolina) lunch counter in 1960. Student activists adopted the tactic later in the decade in demonstrations against the Vietnam War.