TASK DEFINITION: In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.
PROBLEM: Question: What do you call the hard case that surrounds the soft parts of some animals? Answer: exoskeleton

SOLUTION: You call the hard case that surrounds the soft parts of some animals the exoskeleton.

PROBLEM: Question: Which crust lies deep inside the ocean? Answer: oldest

SOLUTION: Oldest crust lies deep inside the ocean.

PROBLEM: Question: Which of the following best describes a mineral? Answer: a solid natural material with a crystal structure

SOLUTION:
A mineral is described as a solid natural material with a crystal structure.