A cathode ray tube is made of glass with a small amount of some kind of gas in it. It has metal electrodes at each end to pick up an electric current. The electrodes are named "positive” and "negative,” which were words used by Benjamin Franklin in the 1700s to describe electricity. A bright ray forms in the gas when an electric current is applied to metal electrodes. In the 1800s, an important scientist suspected that the negatively charged particles in a cathode ray were present in all atoms.

What procedure would allow that scientist to investigate this idea?

a.)observing if the cathode ray forms when the electric current is off
b.)making cathode ray tubes out of different materials to see if the ray is the same
c.)using different magnets to see if the cathode ray responds in the same way to each
d.)changing the strength of the electric current and observe how the ray forms and changes