Let a, b and c be three unit vectors, out of which vectors b and c are non-parallel. If α and β are the angles which vector a makes with vectors b and o respectively and \(a \times \left( {b \times c} \right) = \frac{1}{2}\;b\), then |α – β| is equal to

• A. 30°
• B. 45°
• C. 90°
• D. 60