In the Fehling's solution test for an aldehyde, the red precipitates is due to the formation of

In the Fehling's solution test for an aldehyde, the red precipitates is due to the formation of cuprous oxide

In this test, Fehling's Reagent or Solution is used to heat aldehyde. This process will then produce a precipitate that is reddish-brown in colour. This results from the aldehyde being oxidised in the solution, which also results in the formation of the carboxylate anion.

Hence option D is correct