19. This question is based on the following paragraph. The sentences are numbered to help you answer the question. (1) Earth's crust is made up of relatively rigid plates that ride atop Earth's hot, semiliquid mantle. (2) The plates are called tectonic because they're in constant motion. (3) They can move because Earth's mantle is a very hot and semiliquid fluid called magma. (4) Volcanoes are a result of magma rising up or erupting through a plate, particularly where plate boundaries are moving against each other. (5) Also, when plates slide against each other, causing friction along adjacent plate boundaries, earthquakes frequently occur. (6) Therefore, we often find volcanoes and earthquakes along plate boundaries. (7) Plates may also collide. (8) When that happens, mountain ranges are formed. (9) For example, the collision of the plate carrying the Indian subcontinent created the Himalayan Mountains when it collided with the Asian plate. Which statement about this paragraph is accurate? A. The author uses comparison and contrast to organize ideas. B. There is no single topic sentence. C. There are no supporting details for the main idea. D. The topic sentence is the found in the last line.

Throughout the paragraph there is no single topic sentence found. Although each of the 9 sentences of the paragraph follow a shared topic or theme, none of the sentences can be used as a single topic sentence. A single topic sentence is defined as the most important sentence in a paragraph as it helps to summarize all of the information the paragraph presents. While not always necessary, usually topic sentences can be found at the beginning of the paragraph, in some way working as the introduction statement.