A(n) is an instrumental piece that typically introduces an opera.
counterpoint
oratorio
overture
program music

in "letter from a birmingham jail," king argues that there are four basic steps in any nonviolent campaign: "[c]ollection of the facts to determine whether injustices exist; negotiation; self purification; and direct action." finally, direct action is taken and acts such as boycotts and sit-ins are staged.

explanation:

it refers to the definition of full-contact sports, where the condition is that the sport must have athletes must "purposely collide with each other