Correct option is B

∠ABO = ∠OAB= 40° (opposite angles of the equal sides are equal)
∠ACO = ∠OAC = 30° (opposite angles of the equal sides are equal)
∠BAC = 40 + 30 = 70°
Angle made on centre is two times angle made on circumference by the same arc.
∠BOC = 2 × 70 = 140°