Clemmensen reduction is the reduction of carbonyl groups of aldehydes and ketones to methylene groups under acidic conditions.

-CH(OC2H5)2 is an acetal, which can be hydrolyzed into aldehydes and alcohols under acidic conditions, namely:

CH3COCH2CH(OC2H5)2+H2O——[H3O(+)，δ]—→ch 3c och 2 CHO+2 C2 H5 oh

Exercise may only pay attention to the change of CH3COCH2CHO, but ignore the hydrolysis of ethanol.