Please explain why this answer is correct. This doesn't seem like speech here, but it is.

The Federal Family Film Enhancement Act assesses an excise tax of 10% on the price of admission to public movie theaters when they show films that contain actual or simulated scenes of human sexual intercourse. Which of the following is the strongest argument against the constitutionality of this federal act? The act imposes a prior restraint on the freedom of speech protected by the First Amendment. The act violates the equal protection concepts embodied in the Due Process Clause of the Fifth Amendment because it imposes a tax on the price of admission to view certain films and not on the price of admission to view comparable live performances. E The act is not rationally related to any legitimate national interest. The act imposes a tax solely on the basis of the content of speech without adequate justification and, therefore, it is prohibited by the Freedom of Speech Clause of the First Amendment