Final answer:
Senator Edmund G. Ross faced various pressures during President Andrew Johnson's impeachment trial, including party threats, promises of political rewards, and public opinion, leading to the answer D. All of the above.
Step-by-step explanation:
Some of the pressures faced by Senator Edmund G. Ross during President Andrew Johnson's impeachment trial included threats of expulsion from the Republican Party, promises of future political favors and positions, and public opinion and potential backlash from constituents. Specifically, Ross encountered significant pressure from fellow Republicans to vote for Johnson's removal, including threats that he would be ostracized from the party. He also faced the allure of political rewards for voting 'guilty'. Moreover, public opinion played a role, with the potential for negative reactions from voters depending on his vote. Hence, the answer to the question about the pressures faced by Ross that influenced his vote regarding Johnson's impeachment is D. All of the above.