The lignins are macromolecules that are major components of the many types of wood, where they bind

Question:

The lignins are macromolecules that are major components of the many types of wood, where they bind cellulose fibers together in these natural composites. The lignins are built up out of a variety of small molecules (most having phenylpropane skeletons). These precursor molecules are covalently connected in varying ways, and this gives the lignins great complexity. To explain the formation of compound B below as one of many products obtained when lignins are ozonized, lignin model compound A was treated as shown. Use the following information to determine the structure of B.