Q: You are given a passage. Using the information present in the passage, you need to classify it into one of the 10 topics: 0 - 'Society & Culture', 1 - 'Science & Mathematics', 2 - 'Health', 3 - 'Education & Reference', 4 - 'Computers & Internet', 5 - 'Sports', 6 - 'Business & Finance', 7 - 'Entertainment & Music', 8 - 'Family & Relationships', 9 - 'Politics & Government'.
California electricity is generated by several sources, including hydroelectric, wind, geothermal and nuclear (in addition to the more traditional natural gas). The question is why these other sources aren't used more, and the answer is that historically, they've either been more expensive or have environmental risks of their own (esp. for nuclear). As petroleum and natural gas sources start to get used up, and world demand for energy increases, the cost of electricity from natural gas will go up and the other sources will become more cost effective and more prevalent.
Incidentally, solar power is another source used in California, but it's provided by individuals, not power companies. If your house has solar power and you have the right equipment, you can sell your surplus electricity to the power company and your electric meter will literally run backward.
A:
9