D is the correct answer.
Vice Presidents are often chosen based on geographic or policy considerations and a good VP candidate will give the President strength in an area that they are weak in.
D. is the correct answer.
A presidential candidate will try to select a vice presidential candidate that will mean that the more people over the entire country will vote for them. As such, "balancing the ticket" is an activity that will make the pair of candidates more attractive to more people. With that in mind, let's look at the options and see what does and does not make sense.
A. A presidential candidate chooses a vice presidential candidate who shares his viewpoint on major political issues.
This action does increase the appeal to those who are already inclined to vote for the presidential candidate, but doesn't increase the appeal outside that group. So this is a bad choice.
B. A presidential candidate chooses a vice presidential candidate from another political party in order to gain votes from both sides.
This would most certainly increase the appeal. But it would also cause problems that the 12th amendment was intended to prevent due to the results from the elections of 1796 and 1800. And if those problems were considered severe enough to warrant a constitutional amendment, it's a pretty strong indication that this would be a "bad idea". So this too, is a bad choice.
C. A presidential candidate chooses a vice presidential candidate who has administrative experience in order to support the president.
Let's rephrase this choice "choose a vice president who would act like a common secretary." Anyone could serve that function and many better than politicians. So this is a bad choice.
D. A presidential candidate chooses a vice presidential candidate who has voter support in geographic areas that the presidential candidate does not.
This increases the population base that will support the candidates. Where the presidential candidate doesn't have support, the vice presidential candidate will. And many will believe that the president will accept advice and insight from the vice president. So this does help "balance the ticket" and is therefore the correct choice.