Association forms print a choice as several options with initials slots — "the Property was constructed ___/___ prior to 1978, OR ___/___ during or after 1978".
To set it up: select every initials box in the choice, then Make these mutually exclusive. Printed rows become the options automatically — a row is one choice, and its two slots (one per client) appear and disappear together.
What the signer gets: initialing one option clears the others.
The part worth understanding: the choice belongs to the document, not to each person. The first party to commit takes it, and anyone signing later is held to that — the ruled-out options grey out and say who took it. Two sellers picking different construction dates would produce a contradictory contract, so that can't be allowed.
Whoever gets there first can still change their mind before they submit. It's only locked for the people who come after.