The correct answer is D. You don't have to reimburse me for dinner; it's my treat.
Step-by-step explanation
The semicolon (;) is a punctuation mark made up of a period superimposed on a comma. Experts consider the use of this sign to be subjective. One of its main uses is to separate sentences with semantic relationships, which is used when two sentences are joined without a conjunction. An example of this is "You don't have to reimburse me for dinner; it's my treat" because it is separating two sentences that do not have conjunction that relates them, but that are related. So the correct answer is D. You don't have to reimburse me for dinner; it's my treat.