C because you can't control the sun moving across the sky and therefore is not testable in an experiment.
The answer is D i took the test but got it wrong but i got to see the answers
That change would most likely cause the current at every point in the circuit
to decrease by 83-1/3% ( 5/6 ) of its original value. Also, the voltage across
each component of the circuit ... resistor, light bulb, motor, open switch etc. ...
would become 5/6 less.