instruction:
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.
question:
Fact 1: the number of rings in a tree trunk can be used to estimate the age of the tree. 
Fact 2: If you want to find the age of a forest, you find the tree with the highest number of tree rings.
answer:
to estimate the age of a forest, find the tree with the highest number of rings.


question:
Fact 1: the mass of an object causes the gravitational force exerted by that object. 
Fact 2: Gravity accelerates mass.
answer:
gravitational force accelerates objects.


question:
Fact 1: seat belts are used for preventing injuries to passengers in cars. 
Fact 2: Seat belts save lives .
answer:

Preventing injuries to passengers in cars saves lives.