Why do we control the variables we are not investigating

Aflashlight produces light using energy from the batteries. in which order does the energy change form? a. from chemical to electric to light energy b. from electric to light to chemical energy c. from electric to chemical to light energy d. from light to electric to chemical energy

Which kingdom includes some organisms that have no nucleus and can live in an environment with an extremely high salt content

Has anyone taken the genetics unit test in connexus? not looking for answers, just a little bit what to expect and some with studying.