A stanza that suddenly shrinks to two lines after a nine-line stanza creates what kind of effect?

A stanza that suddenly shrinks to two lines after a nine-line stanza creates what kind of effect?
a.
It enacts enjambment by pulling the longer stanza's meaning into what follows
b.
It creates emphasis through contrast, making the brief stanza feel significant
c.
It introduces a volta by bringing the poem's central tension toward resolution
d.
It signals a transition from fixed form conventions into free verse