The correct answer to this question is C. There are a few states for which Option A is correct. B and D are completely incorrect.
The Electoral College is created by the Constitution. A state cannot simply do away with the Electoral College simply because it wants to do so. This means that Option B cannot be correct. Proportional representation is a system in which the votes in a given district are split up and given to different candidates depending on the percentage of the votes that they got. In other words, if the Democrat got 40% of the votes and the Republican got 60% of the votes in a given state, the Democrat would get 40% of the electoral votes. This is not a system that is used in the US.
Some states do use Option A. Specifically, Maine and Nebraska do so. However, they are the only states that do this so Option A is not correct.
That leaves Option C. Almost all states give all of their electoral votes to whoever wins the popular vote in the state. This means that a candidate can win the popular vote by just a few votes (as happened with President Bush in Florida in 2000) and can get all of the electoral votes for the state.