A formal letter follows a specific format and alignment style. The name and address of the sender and receiver are written according to standard letter-writing conventions.
Step 1: Understand the format of a formal letter.
In a formal letter, all parts such as the sender’s address, date, receiver’s address, subject, salutation, and body are generally aligned to the left side of the page.
Step 2: Analyze the options.
(A) Right margin: Formal letters are not written aligned to the right side.
(B) At the bottom: The name and address are not placed at the bottom of the letter.
(C) Left margin: This is correct, as formal letters follow left alignment format.
(D) Middle: The address is not written in the middle of the page.
Step 3: Conclusion.
Since formal letters follow left alignment, the correct answer is (C).
Final Answer:
\[
\boxed{(C) \, \text{Left margin}}
\]