What is a carpetbagger?
a. a northern republican who participated in state conventions in the south
b. a northern white who agreed with the abolishment of slavery
c. a southern white who supported reconstruction
d. someone who had betrayed the united states during the civil war

The most fitting answer is A.

After the American civil war, some Northerners moved  over to the South during the Reconstruction period of 1865 - 1877.  Many of these newcomers to the South usually carried a form of cheap luggage bags called carpet bags.  White Southerners did not trust their intentions and nick named them carpetbaggers, a term that was used with a derogatory intent.

"Carpetbaggers" in general supported measures aimed at democratizing and modernizing the South and about 60 of them were elected  to congress and included a majority of Republican governors in the South during the reconstruction period.