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: Mammals generate heat mainly by keeping their metabolic rate high. 
Fact 2: Shrews have the highest metabolism of any mammal.

SOLUTION: Shrews generate the most heat by keeping their metabolic rate high.

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: the mass of a planet causes the pull of gravity on that planet. 
Fact 2: Gravity is the pulling force that holds objects to the surface of a planet.

SOLUTION:
The mass of a planet causes the pulling force that holds objects to its surface.