Which two organic compounds share a functional group?

Both Octane and Propane have the same functional group (Alkanes)

Both Ethene and Propene have the same functional group (Alkenes)

Both Ethyne and Butyne have the same functional group (Alkynes)

Both Ethanol and Propanol have the same functional group (Alcohol)

Both Ethanoic Acid and Propanoic Acid have the same functional group (carboxylic acid)