sentence2_structure: Fracking<>delivers<>natural gas<>from rock$$$rock<>might not otherwise be<>obtainable
sentence1: Batali is a critic of hydraulic fracturing, commonly known as fracking, a method of natural gas extraction.
sentence2: Fracking delivers natural gas from rock that might not otherwise be obtainable.
question: What delivers natural gas from rock that might not otherwise be obtainable?