Answer:
A. The Fugitive Slave Act
Step-by-step explanation:
A is correct as it allowed slave owners to reclaim runaway slaves.
B is also not correct as after the war California entered Union as a free state and many other state had the opportunity to choose whether they would prohibit slavery.
C is not correct as it ended the slave trade.
D is not correct as according to it slavery was prohibited north of the southern boundary of Missouri.