Using a mixture of water, sand, and chemicals under high pressure to free tightly held oil and natural gas is known as . a. mud drilling b. high density pumping c. rotary drilling d. hacking e. fracking

E. Fracking.

Explanation:

Fracking is also called hydraulic fracturing, which is the process of creating fractures in rocks and rock formations by injecting specialized fluid into cracks to force them to open further.

It is also the process of drilling down into the earth before a high-pressure water mixture is directed at the rock to release the gas inside. Water, sand and chemicals are injected into the rock at high pressure which allows the gas to flow out to the head of the well.