Why aldoses react with Fehling solution and `PhNHNH_(2)`, but not with `NaHSO_(3)`?

Fehling solution is

Fehlings solution is

Which does not react with Fehling's solution?

Tollens vs Fehling Solution

Assertion : Glucose reacts with phenyl hydrazine and Fehling's solution but not with NaHSO_(3) . Reason : NaHSO_(3) cannot break the ring structure.

What are the following: Fehling's solution

The acid which reduces Fehling solution is

How does formaldehyde react with : Fehling's solution