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.

Fact 1: Constriction occurs when the muscular walls of blood vessels contract. 
Fact 2: Dehydration causes vessels to constrict and blood to thicken.
Constriction causes blood to thicken.

Fact 1: boiling is when liquids are heated above their boiling point. 
Fact 2: If the pressure is reduced, the boiling point is lowered.
Less heating is required to make a liquid boil if the pressure is reduced.

Fact 1: a greenhouse is used to protect plants by keeping them warm. 
Fact 2: Energy from the sun keeps the earth warm, enables plants to grow.

Greenhouses are used to protect plants using the energy from the sun.