75% of China's electricity comes from coal, and only 2.5% comes from oil. Because most of the oil is drunk by cars, the cost of coal transportation is high, and at least half of the capacity of China's railways is used for coal transportation. At present, coal inventory in many thermal power plants Can't persist for a week, and if there is a problem with rail transportation, the direct consequence is to pull the brakes. The above text is intended to emphasize? ['The proportion of using petroleum to generate electricity should be increased to regulate risks.', 'There are drawbacks to the electricity production structure that relies too much on coal.', 'The smoothness of railway transportation is related to the production of many thermal power plants.', 'Coal power generation increases the burden of rail transport.']