Mary and William had to 4) Agree to and sign the English Bill of Rights to ascend the throne.
Once the Glorious Revolution in England was over in 1688 (which resulted in King James II abdicating and fleeing the country), the Parliament, who had taken over the power, drafted a Bill of Rights, and required Mary II (the daughter of James II) and William III (Her husband) to sign it in order to be proclaimed officially King and Queen.
At the moment, the parliament and the people were fed up with the previous kings' tyrannical rule. The document was an attempt to stop the injustices, to limit the king's powers, to have a more strong and active Parliament in the reign's decision and bring more justice to civilians. Mary II and William III accepted to sign the English Bill of Rights in 1689.