Which sentence correctly uses a comma to separate the introductory phrase?

A. The Library of Congress is the largest library in the world, because it contains more than 147 million items.

B. The largest library in the world is the Library of Congress, which contains more than 147 million items.

C. The Library of Congress, which is the largest library in the world, houses over 147 million items.

D. Containing more than 147 million items, the Library of Congress is the largest library in the world.

The correct sentence that uses a comma to separate the introductory phrase is: The Library of Congress, which is the largest library in the world, houses over 147 million items.

Explanation:

The correct sentence that uses a comma to separate the introductory phrase is:

The Library of Congress, which is the largest library in the world, houses over 147 million items.

An introductory phrase is a group of words at the beginning of a sentence that provides context or background information. In this case, the phrase is "which is the largest library in the world." By using a comma before and after this phrase, we set it apart from the rest of the sentence.