Read the following paragraph and underline the topic sentence. The very act of stepping outside of your comfort zone is critical to your success. Our brains are wired so that it’s difficult to take action until we feel at least some stress and discomfort. In fact, performance peaks when we’re well out of our comfort zone. If you’re too comfortable, your performance suffers from inaction; if you move too far outside of your comfort zone，you melt down from stress. Stepping outside of your comfort zone makes you better, and it doesn’t have to be something as extreme as climbing Mount Everest. It’s the everyday’s challenges that push your boundaries the most, none of which require a flight to Nepal. Just embrace these challenges since no one has ever accomplished anything remarkable when comfortable.
【正确答案】：The very act of stepping outside of your comfort zone is critical to your success.
【题目解析】：本段文字主要是从反正两方面来讲述走出舒适区的重要性和对走出舒适区的正确理解。走出舒适区会使你做出更好地表现，但走出舒适区也绝不是挑战极限而是迎接每天的挑战。所以本段文字的第一句其实就是文章总起句，也是文章的主题句。
