What supreme court case established the clear and present danger doctrine?

Which situation would be considered an example of the freedom of association? a. three students write a letter to a local newspaper demanding that a teacher be fired. b. a group forms on a college campus to support a particular political candidate. c. an individual purchases a membership to a local gym. d. a religious organization buys several local lots in order to construct a new church building.

Don’t mind the already marked answer but taking it now

The answer because i don’t know it someone