How Did Scientists Determine That the Shoot Apical Meristem (SAM)

How did scientists determine that the shoot apical meristem (SAM) is genetically controlled?

A) They used Arabidopsis because its entire genome is known.
B) They used a dwarf Arabidopsis that has a dwarf meristem.
C) They discovered that the central zone cells of Arabidopsis do not function normally.
D) They discovered that the central zone cells of Arabidopsis differentiate very quickly.
E) Arabidopsis was not involved in this study.