The government can ban speech if the speech advocates the breaking of criminal laws or encourages other illegal activity:

question 3 options:

a. if the speech can endanger national security if the government uses the least restrictive means to prohibit the speech and permits the portions of the speech which does not endanger national security.

b. if the speech advocates illegal activity if such activity presents a clear and present danger to national security such as encouraging people to avoid the draft.

c. if the speech will lead to imminent lawlessness or it is so provocative to the audience that it is a fighting word which is a kind of insult so severe that an average addressee will want to fight.

d. if the speech encourages physical or sexual abuse of children or the disabled.