The correct answer is (A) To worry about; to meditate on or over (esp. insults, ill designs, etc.) to think about sullenly, particularly after a perceived insult or injury. To focus on a subject silently and obsessively.

Brood comes from Old English brod, Danish broed, German brut.

Examples of use:

• He was inclined to brood excessively over his apparent grievances.
• She brooded over the problem for days.