A strong topic sentence is thorough and lengthy.
specific and concise.
general and brief.
scientific and detailed.

Consider the text from "machu picchu: a city in the sky” and its central idea. informational text: every year, thousands of tourists come to peru to see machu picchu. to reach machu picchu, tourists can hike along the famous inca trail. the trail covers twenty-six miles. it winds through beautiful mountains, forests, and jungle. visitors can also take a bus or train ride up to the ruins. the train takes you past miles of farmland along the urubamba river valley. above are the andes mountains. the tops of the mountains are often covered with mist. then, the train goes up a mountain on a winding road. the road climbs almost 1,640 feet. other incan ruins can be seen beside the road. most are very small compared to the city ahead. central idea: tourists enjoy visiting machu picchu in the mountains of peru. what supporting detail is most important to include in a summary of this text? people can hike the inca trail or take a train or bus to reach machu picchu. when people travel to machu picchu, they see miles of surrounding farms. people are surprised by the mist on the peaks of the andes mountains. when people visit machu picchu, they sometimes see other smaller ruins.