Wich pair of molecules both contain carbon atoms ?

Which of the following is not a product of the second stage of glycosis

Lactase is essential for digesting lactose in milk. this enzyme is specific for this sugar. why? molecules and active sites vary in size; only properly sized molecules can fit. there is a precise compatibility between the active site and the lactose molecule. specificity refers to the action of the enzyme, such as hydrolysis, and relatively few molecules can be hydrolyzed. reaction-specific enzymes assume a fit by folding around the most numerous substrate molecules.

The backbone of the double helix has an alternating molecules. what do you call these alternating molecule?