If `hat(a),hat(b)` and `hat(c )` are three unit vectors, such that `hat(a)+hat(b)+hat(c )` is also a unit vector and `theta_(1),theta_(2)` and `theta_(3)` are angles between the vectors `hat(a),hat(b),hat(b),hat(c)` and `hat(c),hat(a)`, respectively, then among `theta_(1), theta_(2)` and `theta_(3)`

Options

A. all are acute angles
B. all are right angles
C. at least one is obtuse angle
D. None of these

Answer

C