The cork is impervious to water due to

During secondary growth of plants,stem phellogen cuts off cells on both sides. The outer cells get differentiated into ...$A$... and the inner cells get differentiated into ...$B$... cortex.
Choose the correct combination of $A$ and $B$ with reference to the above statement.

Read the components $a$ to $d$ given in the note and identify the correct sequence of components from the outside to the inside of a mature stem:
$(a)$ Secondary cortex
$(b)$ Wood (Secondary xylem)
$(c)$ Secondary phloem
$(d)$ Phellem (Cork)

An example of monocots showing secondary growth in stems is

Growth rings are generally well marked in trees growing in

The interfascicular cambium develops from the cells of -