Comparative adjectives are used to compare two or more things or people. They are formed by adding '-er' to the end of the adjective or by using the word 'more' before the adjective. In this given sentence, the comparative adjective is 'darker'.

Explanation:

- The young man looked at the clock again, and his face grew darker.

1. Comparative Adjective:
The word 'darker' is the comparative adjective in this sentence. It is used to compare the darkness of the young man's face at two different points in time. It shows that his face became more dark or intense.

Comparative adjectives modify the noun they are describing and provide additional information about a quality or characteristic. In this case, the adjective 'darker' modifies the noun 'face' and provides information about its intensity or darkness.

The other options:

2. The:
The word 'the' is an article, not a comparative adjective. Articles are used to specify or identify a noun. In this sentence, 'the' is used before 'clock' to indicate a specific clock.

3. Young:
The word 'young' is an adjective, but it is not a comparative adjective in this sentence. It describes the age or youthfulness of the man, but it does not compare him to anything else.

4. Man:
The word 'man' is a noun, not a comparative adjective. It refers to an adult male person and does not compare him to anyone or anything else.

In conclusion, the comparative adjective in the given sentence is 'darker'. It compares the darkness of the young man's face at two different points in time.

Darker