Cis-Trans Isomerism Occurs When

Cis-trans isomerism occurs when

A) a branched alkane has a halogen added to two adjacent carbon atoms.
B) an alkene is hydrated according to Markovnikov's Rule.
C) the carbons in an alkene double bond each have two different substituent groups.
D) the carbons in the para position of an aromatic have the same substituent groups.
E) hydrogen is added to both of the carbon atoms in a double bond.