Related Clues:

• One of two slithered dropping LSD
• 1 of 2 or 1 in 3, roughly?
• The one or the other unit covered in solvent
• 'Whichever works'
• Article in Ireland abridged: any one of two?
• That one or this one
• Disjunctive conjunction
• "Whichever"
• "Both will do"
• Flexible reply to "Which one?"