Option C is the correct answer because 'out of the blue' means 'unexpectedly'. Thus, option C is the correct meaning of the given idiom.
Option A is incorrect because 'angrily' means 'to show anger' whereas 'out of the blue' means 'unexpectedly'. Thus, option A is not the correct meaning of the given idiom.
Option B is incorrect because 'quietly' means 'silently' whereas 'out of the blue' means 'unexpectedly'. Thus, option B is not the correct meaning of the given idiom.
Option D is incorrect because 'revengefully' means 'something harmful done in return of a hurtful situation' whereas 'out of the blue' means 'unexpectedly'. Thus, option D is not the correct meaning of the given idiom.