Touch screens often go “dead”—become sluggish and less responsive—after a few months of intense use. The touch screen manufacturer reasoned that dirt and oil, rather than changes in the material properties of the screen, were responsible for the outcome. Which of the following investigations is most likely to yield significant information that would help to evaluate the touch screen manufacturer’s reasoning?

Determining if a special type of glass is used to make the screens of the touch screen devices

Determining whether teenagers make their touch screens go dead faster than other users

Determining whether identical screens, of the same thickness, go dead at different times when used with different brands

Determining whether a dead screen and a new screen produce different responses to the same stimulus

Determining whether smearing various substances on new touch screens causes them to go dead