The example of a 'complimentary close' in a letter is:"Yours faithfully".

Here's why:

• A complimentary close is the formal sign-off used at the end of a letter, expressing respect and good wishes towards the recipient.
• "Sir/Madam" is the salutation, not the closing.
• "Subject line" is the brief summary of the letter's topic, not the closing.
• "Enclosures" refers to any additional documents attached to the letter, not the closing.