Companion cells are thin-walled cells found in:

• A
  Phloem elements where substances are transported towards other plant parts.
• B
  The endodermis of the root for rapid water transport from the cortex to the pericycle.
• C
  The seed coat to facilitate the emergence of the developing embryonic axis during germination.
• D
  The central part of the style through which the pollen tube grows towards the ovule.