Answer: 4. campaign in each of the 50 states
Step-by-step explanation:
The electoral college was made so that the small states would also have some representation in the elections, so that the most popular states wouldn't run the elections (rules out 1)
The House of Representatives has nothing to do with the electoral college (rules out 2)
The candidates choose their electors, and voters vote for the electors that the candidates chose (so for example, if you vote for trump on the ballot, you're actually voting for the electors that trump chose), so there is no need to persuade the electors that you chose (rules out 3)
Number 4 is correct. The electoral college was made so that candidates wouldn't just go to half-a-dozen states and win the election; they needed to appeal to a wide variety of people in a lot of states.