I think it would be "them"
The Answer would be "The variety in nature"
Answer:
Hazel and Augustus meet at Support Group and bond over literature. They discuss poetry, books, and the meaning of life and death. Hazel has accepted her fate of early death, but worries how her parents will handle it. Gus fears he’ll die without accomplishing something great and leaving his mark on the world.
Explanation:
Use? 'U' makes the same sound as the word use, and it fits in the letters.