TASK DEFINITION: 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.
PROBLEM: Fact 1: Some parasites kill their host, but most do not. 
Fact 2: Tapeworms are internal parasites of vertebrates.

SOLUTION: most tapeworms do not kill their host.

PROBLEM: Fact 1: hearing is used for sensing sound by animals. 
Fact 2: An ear improves hearing.

SOLUTION: Most animals have ears.

PROBLEM: Fact 1: Platypus females lay their eggs in a burrow. 
Fact 2: Like the platypus, it is an egg laying mammal.

SOLUTION:
some mammals lay their eggs in a burrow.