The correct answer and what Antonio means in his speech to Sebastian in William Shakespeare's "The Tempest" is A. Sebastian now has the opportunity to take future into his own hands.
In Act 2, Scene 1, only Antonio and Sebastian remain awake after a solemn music plays. It is then that Antonio delivers his speech trying to convince Sebastian to kill Alonso and become king. Antonio says that it is the opportunity and he should seize it: Th' occassion speeks thee, and my strong imagination sees a crown dropping upon thy head. Now that they accept that Ferdinand has drowned, Sebastian could seize the crown if he acts and murders Alonso.