The correct answer is A) He tried to send something through the mail illegally.
According to the bolded lines, one reason for Schenck’s indictment was that he tried to send something through the mail illegally.
We are talking about the case Schenck v. the U.S., which was decided on March 3, 1919. The Supreme Court unanimously decided that the Espionage Act did not represent a violation of the First Amendment to the United States Constitution and that Congress had the authority to make it valid during times of war.