Nhận biết (M1)

Naledi Motaung and colleagues showed that a low direct-current electrical field laid across graphite — a conductor — together with a gel of acrylamide (AAm) can make materials cling to one another more strongly. At certain voltages the adhesion strength — the stress in kilopascals (kPa) needed to pull the materials apart — ran high, above 30 kPa. Applying a direct-current field of positive voltage does not on its own bring stronger adhesion, though, as is clear from the fact that ______

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

• A.

  mean adhesion strength stood at 0 kPa when no voltage was applied.

• B.

  mean adhesion strength peaked at 3 V, reaching roughly 30 kPa.

• C.

  mean adhesion strength at 2 V fell below what it was at 1 V and at 3 V alike.

• D.

  mean adhesion strength at 1 V came out at roughly what it was with no voltage at all.