Which of the following is the most effective example of a thesis statement?a.All nations must unite to address the 4 main causes of global warming: natural causes, pollution, increase in population, and deforestation.b.All nations must unite to address the 4 main causes of global warming.c.How can all nations unite to address the 4 main causes of global warming: natural causes, pollution, increase in population, and deforestation?d.Both a. and c. above.