episode "The PTA Disbands" follows a teacher's strike, presenting the situation as harmful to students when the school is forced to hire unqualified substitutes. The season 17 episode "Girls Just Want to Have Sums" addresses single-sex education and deficiencies in female education. Environmentalism Lisa Simpson is portrayed as an environmental activist. Environmentalism is most prominently addressed in the season 12 episode "Lisa the Tree Hugger", in which she develops a crush on an environmental activist and begins tree sitting. Other episodes centering on her environmentalism include the season 21 episode "The Squirt and the Whale", in which she tends to a beached whale; the season 8 episode "The Old Man and the Lisa", in which she attempts to teach environmentalism to Mr. Burns; and the season 14 episode "'Scuse Me While I Miss the Sky", in which she causes a city-wide power outage to combat light pollution. Her environmentalism is also satirized in one episode in which she and Marge travel to help clean an oil spill in Alaska but flee after discovering that the glamorous jobs are taken by celebrities and finding that the work is unpleasant. The Simpsons Movie focuses specifically on environmentalism, with the plot driven by pollution and the actions of the United States Environmental Protection Agency. Lisa's environmentalism is portrayed in contrast to apathy or hostility from other characters. In 2019, environmentalist Greta Thunberg's speech to the United Nations was compared to the role of Lisa. The Simpsons has won several Environmental Media Awards for its treatment of the topic. When creating the show, Groening chose to make Homer work at a nuclear power plant to provide opportunity for environmental commentary. Health The Simpsons has made jokes relating to power held by doctors, including one episode in which Dr. Hibbert expresses support for the pharmaceutical industry while wearing merchandise from several major pharmaceutical companies. In the season 4 episode "Homer's Triple Bypass", Homer attempts to defraud a health insurance provider by giving a false report of his medical history, but he has a heart attack while doing so. In the season 13 episode "Sweets and Sour Marge", Marge applies legal pressure to prevent the sale of sugary food in Springfield, but the ruling proves unpopular and turns Marge's family against her. A 2004 study found that about 40 percent of health-related messages on the show reinforce unhealthy behaviors, including messages relating to poor nutrition, harmful