When sucrose (common table sugar) is treated with aqueous acid, it is cleaved and yields simpler sugars of these types:

For reasons to be studied later, in the use of this procedure for the identification of the sugars incorporated in a saccharide like sucrose, the product mixtures are often treated with sodium borohydride before analysis. What limitation(s) does this put on identification of the sugar building blocks of the starting saccharide?

HO and R OH