sentence2_structure: Fracking<>delivers<>natural gas<>from rock$$$rock<>might not otherwise be<>obtainable
sentence1: Natural gas companies claim that fracking is safe and has gone on for decades, but there are a lot of people who disagree with the safety of fracking operations, and worry about the recent proliferation of fracking.
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?