(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.

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.

anonymous · Answer

What is the topic sentence for this passage?
A. There is no single topic sentence.
B. Sentence 1
C. Sentence 2
D. Sentence 4

xixi743 · Answer

B. A topic sentence is supposed to introduce the topic that is being discussed in the paragraph. It's normally the first sentence.