In Alkenes, There Are Four Groups Bonded to the Carbons

Multiple Choice

In alkenes, there are four groups bonded to the carbons that constitute the carbon-carbon double bond. Which of the following situations produces cis-trans isomerism?

A) when all four groups are the same
B) when the two groups bonded to each carbon atom are different from one another
C) when three of the four groups in an alkene are the same, but the fourth group is different
D) none of these