Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Thorium is a by-product of the extraction of rare earths from monazite sands.
Reason (R): India's Kakrapara-1 reactor is the world's first reactor which uses thorium.
In the light of the above statements, choose the correct answer from the options given below: