Final answer:
The subject of this question is English and the correct answer is RSVP.
Step-by-step explanation:
The subject of this question is English. It is asking about a 4-letter request that is commonly used instead of 'Regrets Only'.
The correct answer is A) RSVP, which stands for 'répondez s'il vous plaît' in French, meaning 'please respond' in English. RSVP is commonly used to request a response from invited guests to an event.
Other options listed are B) TTYL (Talk To You Later), C) ASAP (As Soon As Possible), and D) FYI (For Your Information), but they are not related to the concept of 'Regrets Only'.