Study the sample paragraph below and answer the questions.
There are many reasons why people move. First of all, some people move to find better jobs or to advance their careers. There are more opportunities in bigger cities, so people may have the chance to be more successful in their jobs. Others are attracted to places with better weather. If you’re living in a place with low temperatures in summer, it is a good idea to think about a change in your environment. Still others want to move to a place with less crime. This is because cities with higher crime rates pose a threat to its residents. Finally, people often want to move to a place with a lower cost of living. Life in big cities is generally more expensive than it is in smaller cities. To sum up, every year, millions of people move to new places due to various reasons.
What is the topic sentence?