A dwarf root stock of apple is

Answer: Option A

A dwarf rootstock of apples is M-9 (Malus).
Dwarfing rootstocks produce the smallest trees and range from 6 feet tall to 12 to 14 feet tall.
The malus M-9 are widely used rootstocks for high-density orchards on fertile grounds. Trees grown on this very important dwarf apple rootstock are relatively small in height. A support system, and stakes, are required. First apple production from fruit trees on M-9 can be expected in the second year after planting.