A、He had helped Booth murder Lincoln. B、He had made a diagnostic error. C、He had concealed the facts. D、He had given Booth help

Time and time again, one may be warned, "Your name will be mud." Many have used the expression in the mistaken belief that it has something to do with the kind of dirt found in the streets or on unclean river bottoms. But the expression comes from the name of Doctor Samuel Alexander Mudd, a physician who fixed the broken leg of John Wilkes Booth, the man who killed President Abraham Lincoln. Doctor Mudd treated Booth’s injured leg without knowing who he was. A small group helped Booth to plan Lincoln’s murder. They were all caught and sentenced to death or prison terms. Doctor Mudd had nothing to do with Lincoln’s murder or with any of the men who had planned it. All seemed to show that he was an innocent man. But he had given some kind of help only to leave Booth to escape. This in itself was a crime then. And so, Doctor Mudd was sentenced to prison for life. In prison, Doctor Mudd saved many prisoners and guards in a yellow fever outbreak. President Andrew Johnson pardoned him in 1869, after the doctor had spent almost four years in prison. The American people considered the murder of Lincoln a heavy blow to them. It filled them with bitterness that lasted many years. They hated Booth very much and they also hated anybody who had helped the murderer in any way. Doctor Mudd was freed, but people never forgave him and his name passed into American folk speech as something bad, hateful. The Mudd family had also suffered a lot because of the name until not long ago.
Questions 29 to 31 are based on the passage you have just heard.
29. What does the expression "Your name will be mud" mean, according to tbe passage?
30. Why was Mudd sentenced to life imprisonment?
31. What would have happened to Mudd but for President Andrew Johnson’s pardon?