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.

[Q]: Question: What type of substance is any matter that has a fixed chemical composition and characteristic properties? Answer: pure chemical substance
[A]: Pure chemical substance type of substance is any matter that has a fixed chemical composition and characteristic properties.


[Q]: Question: What holds ionic and covalent compounds together? Answer: electrostatic attractions
[A]: Electrostatic attractions holds ionic and covalent compounds together.


[Q]: Question: What does the thymus gland produce? Answer: t cells
[A]:
The thymus gland produces t cells.