Question

what was the network of secret routes used by african-american slaves to escape to free states or canada?
○ northern express
○ freedom route
○ transcontinental railroad
○ underground railroad

Explanation:

The question asks about the secret network for enslaved African - Americans to escape. The "Underground Railroad" was a network of secret routes and safe houses used by African - American slaves to escape to free states or Canada. "Northern Express" is not a known escape network. "Freedom Route" is a vague term and not the specific historical name. The Transcontinental Railroad was for connecting the US coasts, not for slave escapes.

Answer:

D. Underground Railroad