In a Δ ABC, the bisectors of ∠ B and ∠ C intersect each other at a point O. Then ∠ BOC is equal to :

• 90 ° - 1 ∠A 2
• 120° + 1 ∠A 2
• 90 ° + 1 ∠A 2
• 120° - 1 ∠A 2