Why did colonists feel that slaves were needed to work as farm laborers?

Which of the following statements about the fugitive slave act of 1850 is not accurate. a. marshals who refused to arrest a suspected fugitive could be fined $1,000. b. slave owners had to present evidence that an african american in the north was a fugitive slave. c. any person who provided food or shelter to a fugitive slave could be find $1000 and placed in jail for six months. d. it required all federal marshals to arrest any african-american suspected of being a runaway slave.