A backup contract in Texas becomes the primary contract when:

Option A is incorrect because simply accepting a backup contract doesn't make it primary. A backup contract, by definition, only becomes active when the primary contract fails. Acceptance alone doesn't terminate the existing primary contract.

Option C is incorrect because there is no automatic 30-day conversion period for backup contracts in Texas or most other states. The timing depends entirely on when the primary contract terminates, not a predetermined timeframe.

Option D is incorrect because the removal of contingencies by the primary buyer doesn't automatically terminate that contract or activate the backup contract. The primary contract remains in effect unless properly terminated by other means.