Which invention contributed the most to the increase of the number of slaves in the 1800? a. the railroad
b. the steamship
c. the cotton gin
d. the mechanical reaper

C the cotton gin. It created a greater need for slaves to work.

It’s C

Explanation:

Because of the invention cotton gin by Eli Whitney. His machine of rollers, teeth, and brushes cleaned the seeds out of the cotton very quickly and efficiently. The cotton gin led to more cotton being plated, more and bigger plantations (large farm) and the need for more slave.

It helped separate the seed from the cotton more faster.

Hope that help!

Ithink it is 4. making colonies.