The correct option is C The Principal
Blank 1 must be filled with the recipient of the letter. The recipient is the person to whom the letter is written.
Option B: The Principal is the recipient of the given formal letter (written by a student), as it's mentioned in the passage: "Ramesh writes the following application to the principal". Hence, option 'B' is the correct answer.
Option A: The 'Principle' does not refer to the required recipient here. Since it's spelled differently, 'principle' refers to any fundamental truth or scientific law. It does not refer to the person who runs a school. Hence A is incorrect.
Option C: 'Mr. Ramesh' is the name of the person who has written the letter, whereas the name of the recipient is to be written after 'To'. Hence option C is incorrect.
Option D: The letter is written by Ramesh (first person) to the principal (second person). The doctor is merely mentioned in the letter. He/she is spoken of in the third person. A person in the third person is not spoken 'to', but spoken 'about'. Hence, the doctor is not the receiver of the letter, and option D is incorrect.