A group of researchers investigated the effects of two vocabulary learning strategies on word retention two weeks later. In this example, learning strategy is the variable and word retention is the
variable.

a

explanation:

no diagram was provided, but i'm guessing it's the one i've attached to my answer.

here, a mechanical force turns the rod.   this generates an electric current in the coil, which powers the bulb.

ok

explanation:

it was given as a lesson and guide for prayer.