In which of the sentences below is the word prove used as it is in the second line of the stanza?

A three line stanza is called a tercet. A four line stanza is a quatrain, and a five line stanza is a quintet. Two other common lengths are a sestet, six lines; and an octave, eight lines. For instance, you might break a fourteen line poem into three quatrains and a couplet, or into an octave and a sestet.