Answered

In the ten years following the civil war, a large numbers of former slaves earned a living by becoming

  1. Conductors on the underground railroad
  2. Workers in Northern factories
  3. Sharecroppers on Southern farms
  4. Gold miners in California

Verified Answer :

In the ten years following the civil war, a large numbers of former slaves earned a living by becoming "3. Sharecroppers on Southern farms," since their opportunities for advancement were very slim, and moving to the North was often expensive.