Depends on what the excerpts are
I believe the answer is C. Even though they can all be good.
The comma would end up between but and orange.
"You may have an apple or an orange, but you can't have both."
This is because you're coming to a conjunction, which usually has a comma preceding, or coming before, it.
D Decrease the population of Ireland. From A Modest Proposal "I can think of no one objection, that will possibly be raised against this proposal, unless it should be urged, that the number of people will be thereby much lessened in the kingdom."
