Vascular cambium is one of two lateral meristems; the other is cork cambium. a plant grows in diameter primarily through divisions of the vascular cambium. if you pull a small piece of bark off a tree and look at the bark's inside surface, what tissue are you looking at (ignore any remaining cells of vascular cambium that may be left)? cork cork cambium xylem phloem

Option D, Phloem

Explanation:

Phloem consists of following parts -  

a) Sieve tubes

b) Companion cells

c) Phloem fibers  

d) Phloem parenchyma cells

Protophloem and metaphloem matures before and after cell elongation respectively. However, As a plant ages , the sieve tubes of protophloem get destroyed as a plant ages while the remaining cells in the phloem converts into fibers. These fibres and later maturing metaphloem appear as tissue with in the bark of the tree.  

Hence, option D is correct