I'm taking a test and have to guess the right answer to the question after the article. Article: Common indoor plants may prove to be a valuable weapon in the fight against rising levels of indoor air pollution. Those plants in your office or home are not only pretty, but NASA scientists are finding them to be surprisingly useful in absorbing possible harmful gases and cleaning the air inside modern buildings. NASA have announced the finds of a 2-year study that suggested the common indoor plants may provide a natural way of helping fight against "Sick Building Syndrome ". Research into the use of biological processes as a means of solving environmental problems, both on Earth and in space habitats, has been carried out for many years by Dr. Bill Wloverton, a senior research scientist at NASA. Based on preliminary evaluations of the use of common indoor plants for indoor air purification ,NASA funded a study using about a dozen popular varieties of attractive plants to determine their effectiveness in removing several key pollutants linked with indoor air pollution. NASA research on indoor has found that living plants are so efficient at absorbing pollutants in the air that some will be launched into space as part of the biological life support system aboard future orbiting space stations. While more research is needed, Wolverton says the study has shown that common indoor plants can remove certain pollutants from the indoor environment. "We feel that future results will provide an even stronger argument that common indoor plants can be a very effective part of a system used to provide pollution free homes and work places," he concludes. "Combining nature with technology can increase the effectiveness of plants in removing air pollutants," he said. NASA research has always shown that living, green and flowering plants can remove several poisonous chemicals from the air inside buildings. You can use plant in your home or office to improve the quality of the air to make it a more pleasant place to live and work--where people feel better, perform better, and enjoy life more. Question: The main idea of the passage is _ . Options: A: plants are very useful to human beings B: indoor plants can help remove indoor air pollution C: indoor plants should be raised in both homes and offices D: NASA have studied indoor plants for many years
B