Assertion 'a': During casting of aluminium, grain refinement can be achieved by addition of certain alloying elements.
Reason 'r': The addition of the alloying elements may result in the formation of deoxidation products or intermetallic compounds which may act as nucleation sites for grain refinement.

A. Both 'a' and 'r' are true, but 'r' is not the reason for 'a'

B. Both 'a' and 'r' are true and 'r' is the reason for 'a'

C. 'a' is true but 'r' is false

D. 'a' is false but 'r' is true

Answer: Option A