Combine the given two facts to write a concluding fact. Note that there should be some parts of the first and second facts that are not mentioned in this conclusion fact. Your combined fact should be the result of a chain between the two facts. Chains form when two facts connect together to produce a concluding fact. An example of a chain is: "pesticides cause pollution" (fact1) + "pollution can harm animals" (fact2) → "pesticides can harm animals" (conclusion fact). Parts of the concluding fact overlap with the first and the second fact. To construct such a  concluding fact, a useful way is to borrow the subject from one fact and the ending conclusions from another fact.
--------
Question: Fact 1: HIV infects and destroys helper T cells. 
Fact 2: Helper T cells are the critical link in our immune system.

Answer: HIV damages our immune system.


Question: Fact 1: when metal conducts heat , that metal expands. 
Fact 2: Steel is a solution of metals.

Answer: when steel conducts heat, it expands.


Question: Fact 1: Urine is the liquid waste product of the body that is excreted by the urinary system. 
Fact 2: Liquid waste passes through the blood and the urinary system .

Answer:
Urine leaves the body through the urinary system.