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: boulders are formed by glaciers melting sometimes. 
Fact 2: Glaciers are made of snow, ice and rock.

SOLUTION: boulders are formed by snow, ice, and rock melting sometimes.

PROBLEM: Fact 1: sound can be used for communication by animals. 
Fact 2: Sound occurs when a body, such as a vocal chord, vibrates, or moves back and forth.

SOLUTION: Animals may use vocal chords to communicate.

PROBLEM: Fact 1: mineral graphite is used for making pencil lead. 
Fact 2: F.Y.I., graphite is known as a semimetal.

SOLUTION:
A semimetal is used for making pencil lead.