Read the following paragraph and underline the topic sentences.
Hurricanes, which are also called cyclones, exert tremendous power. These violent storms are often a hundred miles in diameter, and their winds can reach velocities of seventy-five miles per hour or more. Furthermore, the strong winds and heavy rainfall that accompany them can completely destroy a small town in a couple of hours. The energy that is released by a hurricane in one day exceeds the total energy consumed by humankind throughout the world in one year.