Step 1: Frame the question.
We want the renewable starting material in the green, enzyme-based adipic acid route designed by Drath and Frost.
Step 2: Recall the old polluting route.
Conventional adipic acid comes from petroleum-based benzene and releases harmful nitrous oxide.
Step 3: State the green alternative.
Drath and Frost used genetically engineered microbes to make adipic acid from a biomass sugar instead of benzene.
Step 4: Name the feedstock.
That sugar is D-glucose, a cheap renewable raw material.
Step 5: Trace the pathway.
Glucose is fermented through the shikimate pathway to cis,cis-muconic acid, which is then hydrogenated to adipic acid.
Step 6: Eliminate the wrong choices.
Benzene is the polluting old feedstock, while fructose and galactose are not the sugars used here.
Step 7: Select the answer.
The correct starting material is glucose, which is option (2).
\[ \boxed{\text{Glucose} \rightarrow \text{Muconic acid} \rightarrow \text{Adipic acid}} \]