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.

Q: 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.

A: to estimate the age of a forest, find the tree with the highest number of rings.
****
Q: Fact 1: water causes refraction of light. 
Fact 2: When light shines through a drop of water or prism, it bends or is refracted inside the droplet.

A: Light is bent inside of water droplets.
****
Q: Fact 1: the vomiting reflex is used to remove toxic material from the stomach before it is absorbed. 
Fact 2: Nicotine excites the vomiting reflex both in the brain and in the nerves of the stomach.

A:
Nicotine causes a vomiting reflex to remove toxic material from the body.
****