The correct answer is:
c. It guaranteed the right to a lawyer, even if the defendant cannot afford one.
The Supreme Court case of Gideon v. Wainwright (1963) held that the Sixth Amendment of the United States Constitution, which guarantees the right to counsel, is applicable to state courts through the Fourteenth Amendment's Due Process Clause. This ruling ensures that defendants in criminal cases are provided a lawyer at public expense if they cannot afford one, thereby expanding due process rights.