D. When they had 60,000 free male voters.
Explanation:
On July 13, 1787, Congress enacts the Northwest Ordinance, structuring settlement of the Northwest Territory and creating a policy for the addition of new states to the nation. The members of Congress knew that if their new confederation were to survive intact, it had to resolve the states’ competing claims to western territory.
In 1781, Virginia began by ceding its extensive land claims to Congress, a move that made other states more comfortable in doing the same. In 1784, Thomas Jefferson first proposed a method of incorporating these western territories into the United States. His plan effectively turned the territories into colonies of the existing states. Ten new northwestern territories would select the constitution of an existing state and then wait until its population reached 20,000 to join the confederation as a full member. Congress, however, feared that the new states—10 in the Northwest as well as Kentucky, Tennessee and Vermont—would quickly gain enough power to outvote the old ones and never passed the measure.
Three years later, the Northwest Ordinance proposed that three to five new states be created from the Northwest Territory. Instead of adopting the legal constructs of an existing state, each territory would have an appointed governor and council. When the population reached 5,000, the residents could elect their own assembly, although the governor would retain absolute veto power. When 60,000 settlers resided in a territory, they could draft a constitution and petition for full statehood. The ordinance provided for civil liberties and public education within the new territories, but did not allow slavery. Pro-slavery Southerners were willing to go along with this because they hoped that the new states would be populated by white settlers from the South. They believed that although these Southerners would have no enslaved workers of their own, they would not join the growing abolition movement of the North.
- From history.com
Basically this means that President Thomas Jefferson made an easier way for the United States to make a territory become part of a state. This was possible by ten territories selecting the constitution of an existing state then they would wait for that state to reach to twenty thousand people in the population. the twenty thousand people would join the confederation as a full member, therefore 20,000 people made 1 member of the constitution. Then, when the population of an existing state reached 5,000 people the residents could elect their own assembly, meaning that when the population of a state grew to five thousand people, they vote a group of people to help the governor decide what to do with the state. When 60,000 settlers lived in a territory, they could draft (summon, recruit) a constitution and petition for a full statehood.
Therefore, part of the ways a territory could become a state is when they have 60,000 free male voters.
<3 Enjoy,
  Dea
