If the shearing stress is zero on two planes, then the angle between the two planes is A. 45° B. 90° C. 135° D. 225°

The correct answer is $\boxed{\text{B) 90°}}$.

Shearing stress is the stress acting parallel to a surface. It is caused by the relative motion of two adjacent parts of a material. The shearing stress is zero on two planes if the planes are perpendicular to each other. This is because the relative motion of two adjacent parts of a material is zero when the planes are perpendicular to each other.

Option A is incorrect because 45° is not a right angle.

Option C is incorrect because 135° is not a right angle.

Option D is incorrect because 225° is not a right angle.