I'm taking a test and have to guess the right answer to the question after the article. Article: A town in Oxfordshire has become the first in the UK to have biomethane gas from human waste piped to their homes for gas central heating and cooking. Up to 200 families in Didcot now receive the gas via the national gas power system. Head of energy and technology at British Gas, Martin Orrill, said customers wouldn't notice any difference as the gas is purified to the highest standard and has no smell. The gas is produced at a sewage treatment works plant in Didcot. The entire process takes only less than three weeks, with the sewage being collected and sent first to settlement tanks. The solid waste material is then fed into digesters, where anaerobic bacteria digest the sewage, with the aid of enzymes to speed up the process. The digestion process produces methane, which can be burned to drive machines to produce electricity, or can be purified and fed into the gas network and piped to homes and businesses. British Gas says supplying the gas rather than electricity is far more efficient since around two-thirds of the energy is lost in producing electricity. Partners in the Didcot project, British Gas, Scotia Gas Networks, and Thames Water, all hope to expand the process to other towns, and other companies such as Ecotricity and United Utilities have also announced biomethane projects being planned. One of these projects, in Manchester, could be supplying 500 homes with biomethane by mid next year. Another British Gas project in Suffolk will provide gas from digestion of brewery wastes to around 235 families. The Didcot project cost PS2.5m and was influenced by promises of government aids aimed at encouraging companies to develop renewable technologies. An EU directive means the UK must ensure at least 15 percent of its energy is from renewable sources by 2020. The UK produces about 1.73 million tons of sewage annually. If all sewage treatment works in the UK were fitted with the technology, they could supply gas for up to 350,000 families. Question: What is the function of the enzymes? Options: A: To digest the solid waste material. B: To help get rid of anaerobic bacteria. C: To help purify the biomethane. D: To speed up the digestion process.
D