The correct answer is D. Some Republicans did not want to upset the balance of government.
This can be the only correct answer, as Senate Democrats were unable to stop the vote from happening. The vote did occur and Andrew Johnson was one vote short of being removed from office.
Along with this, he did not resign from his position as President before the vote. Lastly, the Civil War had already ended several years before the vote on impeachment occurred.
This shows that only D. can be correct.