Choice "D" is correct. When changing from a manual system to a computer system, the controls almost always are different. That does not mean that they are better or are worse, but they certainly are different.
Choice "b" is incorrect. When changing from a manual system to a computer system, internal control "principles" do not change. The principles remain the same; it is the implementation of the principles that is different.
Choice "a" is incorrect. When changing from a manual system to a computer system, internal control "objectives" do not change. The objectives remain the same.
Choice "c" is incorrect. When changing from a manual system to a computer system, control objectives are not necessarily more difficult to achieve. Some will be more difficult, and some will be easier. But, almost always, the specific controls will be different.