Converting a Cis Isomer to a Trans Isomer

Converting a cis isomer to a trans isomer

A) requires nothing. Cis and trans isomers are actually just conformers, so they interconvert all of the time.
B) requires a chemical reaction.
C) requires a physical change such as melting or boiling.
D) requires both a chemical reaction and a physical change.
E) is impossible. There is no way to convert a cis isomer to a trans isomer.