(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. What is the topic sentence for this passage?
A. Sentence 1
B. Sentence 4
C. There is no single topic sentence.
D. Sentence 2
The topic sentence for the paragraph above is A. Sentence 1. A topic sentence is supposed to give the general idea of a paragraph. Sentence 1 briefly describes what and where plates are in the Earth's crust. The rest of the sentences give more detail about tectonic plates.
