One demand of the abolition movement in the 1800s was a. the immediate freeing of all enslaved people. b. the gradual freeing of some enslaved people. c. an increase in the african slave trade. d. a restoration of the african slave trade.

the answer is A.  the immediate freeing of all enslaved people. 
The abolition movement's goal is to eliminate slavery because they deemed it as inhumane and unnecessary.
This movement became stronger after we enter the industrial period in 1800s when machineries could replace the human labors, so slavery was NO longer the most profitable course of action.

The correct answer is A. the immediate freeing of all enslaved people.