Answer:
B. All states splitting their electoral votes between the candidates based on what percentage of the popular vote they won
Step-by-step explanation:
The reason why in the United States a candidate can become president while losing the popular vote is that most states (all of them except Nebraska and Main) allocate their electoral votes based on a winner-takes-all basis: that is, the candidate who obtains a plurality of votes gets all the electors.
If states instead awarded their electors on a proportional basis, it would be mathematically impossible for a candidate to lose the popular vote and still become president.