A、The danger of carbon monoxide poisoning. B、The sources of carbon monoxide poisoning. C、The characteristics of carbon monoxide

Many areas around the world suffer from frequent loss of electrical power. People often must use other sources of power, such as gasoline or fuel. But these other power sources can be deadly if people do not ventilate the area in which they are used.
    The U.S. Centers of Disease Control and Prevention, or CDC, says that about 430 people die every year in the United States from accidental carbon monoxide poisoning. Carbon monoxide is a colorless and odorless gas. All fuel-powered engines produce carbon monoxide.
    [23] Recently, carbon monoxide killed eight family members as they slept in their home in the U.S. State of Maryland. An electric company had cut power to their home because the family owed the company money. They used an electric heater connected to a small gas-powered generator inside the house.
    Patric Breysse is the director of the CDC Agency for Toxic Substances and Disease Registry. He says the signs of carbon monoxide poisoning can be difficult to notice. “The gas has no color. It has no odor or taste. If you happen to be sleeping at the time, all this could happen to you without your knowledge.” [24]Mr. Breysse says that small, movable gas generators are the most dangerous because people can operate them in their homes, or in a boat or even a tent. He says the best way to prevent carbon monoxide poisoning is to learn how to use these gas generators safely. “The number one step is to avoid using them in any enclosed environment like indoor space. The second step is we can encourage people to put small carbon monoxide detectors in their home environments. They are available in many parts of the world, and they are battery-operated...”
    Mr. Breysse adds that deaths from carbon monoxide poisoning are always preventable. Experts say that small generators should always be located outside and at least 4.5 meters from the home. Scientists also warn that long-term contact with low levels of carbon monoxide can lead to difficulty in thinking, memory loss and depression.
Questions 23 to 25 are based on the recording you have just heard.
23. What is the cause of the death of the eight family members?
24. What is the most dangerous for carbon monoxide poisoning?
25. What does the lecture mainly talk about?