Answer :
"A. It relied on safe houses run by northern whites and blacks to move slaves to Canada" is correct, although it should be noted that there were other destinations as well.
The correct option is A
The underground railway was a clandestine network organized in the nineteenth century in the United States and Canada to help African-American slaves escape from the southern plantations to free states or Canada. The name of "Underground Railroad" comes from the fact that its members used railway terms in a metaphorical way to refer to their activities.