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: a delta is formed by deposition of sediment at the mouth of a river by water fanning out. 
Fact 2: Sand is an example of a clastic sediment.

SOLUTION: a delta is formed by deposition of sand at the mouth of a river by water fanning out.

PROBLEM: Fact 1: the gravitational pull of the Moon on Earth 's oceans causes the tides. 
Fact 2: Tides create current.

SOLUTION: The gravitational pull of the Moon on Earth's ocean contributes to ocean currents.

PROBLEM: Fact 1: Cells secrete acids and bases to maintain the proper pH for enzymes to work. 
Fact 2: Enzyme systems efficiency is pH dependant.

SOLUTION:
Cells secrete acids and bases to maintain enzyme systems efficiency.