What Characteristic Gives C₃ and C₄ Plants Their Names

What characteristic gives C₃ and C₄ plants their names?

A) the sequence in which the carbon-containing molecules were discovered
B) the botanically assigned geographic coordinates where the plants are located
C) the first stable carbon compounds that are produced during the second portion of photosynthesis
D) the first carbon compounds that are produced during the light reactions of each type of plant