The civil rights movement began in the 1950s and was led in large part by

Martin Luther King Jr--he became the leader of the Civil Rights movement in 1954. 

Martin Luther King Jr. led blacks in the south through peaceful protest, boycotts, and sit-ins. His leadership began in 1954 and grew after helping to found the Southern Christian Leadership Conference in 1957. 

The answer is challenging and taxing because arduous means when something is hard and tiring and the excerpt provides clear detail why that's the answer

To be honest i thinks its between the first answer and the third answer