instruction:
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: Protozoa make humans sick when they become human parasites. 
Fact 2: Protozoa Toxoplasma gondii Muscles Nematode Trichinella spiralis Protozoa Sarcocystis sp.
answer:
Species of Sarcocystis can parasitize humans and make them sick.


question:
Fact 1: Secondary meristem is located within and around the vascular tissues. 
Fact 2: Secondary growth occurs in the lateral meristems.
answer:

the area where secondary growth  occurs is located within and around the vascular tissues.