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: lakes are formed by precipitation and runoff. 
Fact 2: The Caspian Sea is, strictly speaking, not really a sea but instead the world's largest lake.

SOLUTION: The Caspian Sea was formed by precipitation and runoff.

PROBLEM: Fact 1: a black hole is formed by a high-mass star collapses. 
Fact 2: Fundamentally, a black hole is invisible.

SOLUTION: a star collapsing can be invisible.

PROBLEM: Fact 1: a warm front causes cloudy and rainy weather. 
Fact 2: Cloudy, cool, or rainy weather can cause some algae scums to die.

SOLUTION:
A warm front causes algae scums to die.