what is the topic sentence in this paragraph?
Nearly everyone is familiar with the dark silhouette of the giant saguaro, its arms thrust stiffly out. However, few people have actually seen this awe-inspiring plant in its natural habitat, since it is found only in the desert in the southwest part of the United States. There a visitor may see saguaros as tall as fifty feet. Such a saguaro is probably several centuries old. Saguaros grow very slowly; after ten years a seedling is less than an inch high. Like other cacti, a saguaro is mostly water. A large saguaro may weigh as much as six tons, and as much as 95 percent of that may be water. Only the thin woody ribs inside the saguaro are not filled with moisture. It is this cactus that represents the desert to most people.
Usually the topic sentence is the first sentence of a paragraph. It tells what the rest of the paragraph is about.
What do you think the topic sentence is?