Related Clues:

• Deleted, with 'out'
• Raised one's hand, say
• Marked, as a box
• Selected on a questionnaire, with "in"
• Struck out, as one letter in each of this puzzle's theme answers
• Chose, in a way
• Picked some guide to 'volunteer' for climbing
• Suggested left-hand page spread
• Expressed a choice
• Took part in election
• Made choice -- put wrong mark
• Zealously loving couple initially going out made a mark?
• Crossed, as a box
• Filled in a ballot, perhaps
• Canceled (out)