The resultant stress on a certain plane makes an angle with the normal to the plane

Question

 The resultant stress on a certain plane makes an angle of 20⁰ with the normal to the plane. On

 the plane perpendicular to the above plane, the resultant stress makes an angle of $\theta$ with

 the normal. The value of $\theta$ can be

 (a) 0⁰ or 20⁰                                        (b) Any value other than 0⁰ or 90⁰

 (c) Any value between 0⁰ and 20⁰      (d) 20⁰ only