Which event was a result of the other three?
(1) sit-ins at whites-only lunch counters in
greensboro, north carolina
(2) martin luther king jr.’s march on
washington, d. c.
(3) signing of the civil rights act of 1964
(4) bus boycott in montgomery, alabama

(3) Signing of the Civil Rights Act of 1964

Explanation:

On December 1, 1955, Rosa Parks declined to leave her seat for a white man on a Montgomery, Alabama bus. Her action sparked a year-long Montgomery bus boycott, which stimulated the south´s participation in the national Civil Rights Movement.

On February 1, 1960, four college classmates in Greensboro, North Carolina refused to leave a whites-only table, in a nonviolent demonstration that was replicated in several other states.

On August 28, 1963, Martin Luther King marched along around 250,000 people in The March on Washington for Jobs and Freedom.  

All of these actions, were the preamble for the signing of the Civil Rights Act of 1964 by President Lyndon B. Johnson, barring discrimination due to race, color, sex, religion or national origin.