(a) Compound A undergoes Rosenmund reduction to give compound B with molecular formula $\text{C}_7\text{H}_6\text{O}$. Compound B does not give Fehling's test but reacts with conc. $\text{NaOH}$ to give C and D. Identify A, B, C and D and write all the reactions involved. Write one chemical test to distinguish between compound B and propanone.