Tollen's reagent reacts with free aldehydes.

Structure A is a hemiacetal (reducing sugar) that exists in equilibrium with its open-chain aldehyde form, allowing it to react with Tollen's reagent.

Structure B is a glycoside (methyl glycoside or similar), where the anomeric carbon is locked in an acetal/ketal form with an group, preventing ring opening and aldehyde formation, so it cannot react with Tollen's. Structure C has a cyclic ether oxygen and lacks a free aldehyde group that can be generated under mild conditions, preventing reaction with Tollen's.

Structure D is a hemiacetal form of a reducing sugar with a free anomeric -OH, allowing equilibrium with the aldehyde form and reaction with Tollen's.

Structures B and C do not react with Tollen's reagent.