Possible Clues:

• Beatles: "Two ___ sending postcards, writing letters on my wall"
• "One ___" (Joan Osborne hit)
• Joan Osborne's 'One __'
• ''That makes two __''
• 'Just the Two ___'
• 'That makes two --!'
• ABBA "One ___"
• 'It happens to the best --'
• "Just the Two ___"
• Beatles "Two ___ sending postcards, writing letters on my wall"