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: when an electrical circuit is working properly , electrical current runs through that circuit. 
Fact 2: Electrical circuits require a complete loop through which the electrical current can pass.

SOLUTION: Electricity completes a loop in a circuit to work properly.

PROBLEM: Fact 1: most canyons are formed by flowing rivers through erosion over long periods of time. 
Fact 2: Erosion was monitored by means of erosion pins.

SOLUTION: Canyon changes are tracked with pins.

PROBLEM: Fact 1: rocks interacting with wind over long periods of time causes weathering. 
Fact 2: Erosion happens when water or wind wears away bits of rock.

SOLUTION:
erosion causes weathering over long periods of time.