Final answer:
Under Alabama law, as long as you have registered to vote by the deadline for the runoff race, you may still vote in the Republican Senate run-off.
Step-by-step explanation:
Under Alabama law, the scenario that is true is D. As long as you have registered to vote by the deadline for the runoff race, you may still vote in the Republican Senate run-off. Alabama does not have an open primary system, so party affiliation is relevant in this situation. Crossover voting is also not illegal under Alabama law, meaning that you can vote in the Republican Senate runoff even if you are registered with a different party. However, it is important to note that different states have different laws regarding primary elections, so it is always a good idea to check the specific rules in your state.