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: when a river floods , that river deposits soil in flood plains. 
Fact 2: Soil erosion harms farm and grazing lands and increases flooding and desertification.

SOLUTION: When a river floods, that river harms farm and grazing lands.

PROBLEM: Fact 1: Roots grow in length and width from primary and secondary meristem. 
Fact 2: Growth in girth is caused by other meristems, called secondary meristems.

SOLUTION: Roots grow in length and girth caused by meristems.

PROBLEM: Fact 1: disease has a negative impact on an organism. 
Fact 2: Influenza, or the flu, is a contagious disease caused by a virus.

SOLUTION:
the flu has a negative impact on an organism.