Read this introduction to an argumentative essay about government. An effective system of government protects its citizens. The purpose of government is to ensure the safety of the nation and its residents. While other concerns such as economic growth are important, a government's primary duty is to keep its people safe. Without the concern of defense or self-protection, individuals are able to live in security. Which sentence states the main argument of the essay? A. the first sentence, B. the second sentence, C. the third sentence, D. the fourth sentence ​