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: measuring the hardness of minerals requires scratching those materials. 
Fact 2: Most gem stones are hard minerals.

SOLUTION: You can measure the hardness of a gem stone by scratching it.

PROBLEM: Fact 1: Some viruses have an envelope of phospholipids and proteins. 
Fact 2: Viruses are enveloped by similar membranes.

SOLUTION: viruses have similar membranes.

PROBLEM: Fact 1: an earthquake causes the ground to shake. 
Fact 2: Earthquakes are movements in the Earth's crust.

SOLUTION:
movements in the Earth's crust causes the ground to shake.