when their COF drops below 0.01, two surfaces reach superlubricity.

two surfaces, when their COF drops below 0.01, reach superlubricity.

reaching superlubricity occurs when two surfaces’ COF drops below 0.01.

superlubricity is reached when two surfaces’ COF drops below 0.01.

English

PASSAGE: <div><p>In 2015, a team led by materials scientists Anirudha Sumant and Diana Berman succeeded in reducing the coefficient of friction (COF) between two surfaces to the lowest possible level—superlubricity. A nearly frictionless (and, as its name suggests, extremely slippery) state, <span aria-hidden="true">______</span><span class="sr-only"></span></p></div> QUESTION: Which choice completes the text so that it conforms to the conventions of Standard English?