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Verbal·Information and Ideas·Command of Evidence

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Wenhao Xu and colleagues demonstrated that applying a low direct current electrical field to graphite (a conductor) and an acrylamide (AAm) gel can increase how strongly materials adhere to each other. At some voltages, adhesion strength—as measured in kilopascals (kPa) of stress needed to pull the materials apart—was high (more than $30\text{ kPa}$). But the mere application of a direct current electrical field with positive voltage is not sufficient to cause increased adhesion, as evidenced by the fact that

Which choice most effectively uses data from the graph to complete the statement?

A

at $2extV$, mean adhesion strength was lower than it was at both $1extV$ and $3extV$.

B

at $3extV$, mean adhesion strength reached its highest observed level at approximately $30extkPa$.

C

at $0extV$, mean adhesion strength was equal to $0extkPa$.

D

at $1extV$, mean adhesion strength was approximately equal to adhesion strength at $0extV$.