Suppose a researcher is performing an experiment on children. She tests the children on one level of the independent variable at the beginning of the school year, but cannot return to test the second level until mid-April, when the school year is almost completed. What threat to internal validity may be a problem

The answer is "Maturation".

Explanation:

When we develop and evolve, we go thru a process called maturity. There are many different types of maturity, including physical and cognitive. As people age, our bodies expand and change, and it is called physical maturity. Cerebral maturity is the mechanism by which our sufficient detail increases as people mature. The educators should share, discuss, and agree upon their goals for student accomplishment and advancement.

d is the correct answer.

b is incorrect because it makes food by itself

c is incorrect because us humans don't know how to produce their own food using the sun like plants.

a is incorrect because consumers can depend on carnivores for eating food for consumers to eat the dead organism. same thing with omnivores.