Hint: Fehling's solution does not reacts with ketone
 

Acetone and benzaldehyde both do not react with Fehling's solution. Fehling's solution does not react with ketone and acetone is a ketone. 

Aldehydes that lack alpha hydrogens, such as benzaldehyde or pivalaldehyde (2,2-dimethylpropanal) cannot form an enolate ion and thus do not give a positive Fehling’s test result under usual conditions.
 

• NaHSO₃ → forms bisulphite addition product with both (acetone + benzaldehyde)
• Phenylhydrazine → forms phenylhydrazone with both (carbonyl compounds)
• Grignard reagent → adds to both (gives tertiary alcohol from acetone, secondary from benzaldehyde)
• Fehling’s solution → reacts only with aldehydes (benzaldehyde gives red ppt), does not react with ketones (acetone does not react)