For a territory to be admitted to the union, the first step was for congress to pass
a. the state constitution.
c. a sunshine law.
b. an enabling act.
d. a sunset law.

The best answer is A.

The Northwestern ordinance created in 1787 by congress proposed that instead of adopting the constructs of an existing state, each territory wishing to join the union would have an appointed governor and council. 

When the population reached 60, 000 people, residents could draft a constitution and petition for full state hood. The ordinance  provided for civil liberties and public education within the new territories but did not allow slavery.  New states would be guaranteed equality with the existing states. 

may i ask which amendments?

it reintroduced the two-party system.