In a few words, antithesis is a rhetorical device that you can use to show contrast. It creates balance and helps emphasise the point and makes it memorable.
In the “Blood, Toil, Tears and Sweat” speech, Churchill outlines his vision which is to be victorious and survive no matter what it takes.
In the line “Win or lose, sink or swim, better die than submit to tyranny and such a tyranny”, he uses antithesis as a rhetorical device to whip up enthusiasm for the fight ahead.
D is the correct answer.