Answer: Hi! I think that the best answer here would be D (California).
Step-by-step explanation:
The Library of Congress had this to say in their article Compromise of 1850: Primary Documents in American History: "As part of the Compromise of 1850, the Fugitive Slave Act was amended and the slave trade in Washington, D.C., was abolished. Furthermore, California entered the Union as a free state and a territorial government was created in Utah."
This tells you that California was a state where slavery was outlawed as soon as it joined the US.
If you need a more elaborate explanation, please let me know and I'll try to provide one! Otherwise, have a good day! :)