What is the topic sentence? 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.
Topic sentences are usually the first sentence, although sometimes they are the last sentence. Which one do you think it is in this paragraph?
It is this cactus that represents the desert to most people.
The topic sentence in this passage is: "Nearly everyone is familiar with the dark silhouette of the giant saguaro, its arms thrust stiffly out."
To determine the topic sentence, we look for the sentence that introduces the main idea that will be discussed in the paragraph. In this case, the topic sentence introduces the idea of the saguaro cactus and its familiar appearance.
By recognizing the topic sentence, we can identify the main focus of the paragraph and understand that the following sentences will provide further information and details about the saguaro cactus.