Which of the following is the function of heartwood?

Coastal trees do not show annual rings because:

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.

Diffuse-porous wood is a characteristic of plants found in which region?

$A$: Bark is all the tissues outside the vascular cambium.
$R$: Bark is formed due to the activity of phellogen only.

Assertion : In woody stems,the amount of heart wood continues to increase year after year.
Reason : The cambial activity continues uninterrupted.