Why was andrew johnson acquitted on charges of impeachment?

a. many feared a constitutional crisis because, without a vice president in office, no one knew who would succeed johnson as president.
b. no one would testify against him.
c. johnson’s lawyers assured moderate republicans that he would behave for the rest of his term, so several voted to acquit him.
d. leading radical republican benjamin wade brilliantly managed the president’s defense.
e. ulysses grant urged republicans to acquit johnson because convicting him might hurt grant’s chances in the presidential election.