(A) Aldol condensation of acetone can be catalysed both by acid (or) base. 

(R) $\beta$-  Hydroxy aldehydes readily undergo base-catalysed dehydration.

Aldol condensation of acetone is catalysed by both acid or base to give beta- hydroxy aldehyde but this readily undergoes acid catalysed dehydration. 

Therefore, Therefore, both (A) and (R) are true and (R) is not the correct explanation of (A).

Hence, Option B is correct