Arrange the following in ascending order with reference to the size of the medulla.
A) Dicot root B) Monocot stem 
C) Dicot stem D) Monocot root

All tissues inside the endodermis such as pericycle, vascular bundles and pith/medulla constitute the stele.

Dicot root -pith is inconspicuous.
 Monocot root -pith is large and well developed.
Dicot stem : Numerous rounded, parenchymatous cells with large intercellular spaces which occupy the central portion of the stem constitute the pith.
 Monocot stem : Pith is absent, and the vascular bundles are scattered throughout the ground tissue.