Glucose (C₆H₁₂O₆) Can Exist as Both an Open-Chain Form and a Closed-Ring

Glucose (C₆H₁₂O₆) can exist as both an open-chain form and a closed-ring form. Before 1900, glucose was only thought to occur as an open chain. Now we know that over 99 percent of the time, glucose occurs in the closed-ring form. What possible difference between these forms would give chemists a clue that the open-chain form was not present?

A) Open-chain molecules can form polymers and glucose does not.
B) Only open-chain forms can undergo condensation, which does not occur with glucose.
C) An open chain presents ends with functional groups (in this case aldehyde) , and glucose failed to undergo typical aldehyde reactions; a phenomenon that could be explained by having no end functional group in a ring structure.
D) Because glucose is solid at room temperature, it must have saturated hydrocarbon chains.
E) Glucose could not be "denatured" so it must be a tight chain.