Minimum spacing between horizontal parallel reinforcement of the same size should not be less than A. One diameter B. 2.5 diameters C. 3 diameters D. 3.5 diameters

The correct answer is C. 3 diameters.

The minimum spacing between horizontal parallel reinforcement of the same size should not be less than 3 diameters. This is to ensure that the reinforcement is adequately spaced to provide the required strength and ductility.

Option A is incorrect because it is not a sufficient spacing to provide the required strength and ductility. Option B is incorrect because it is not a common spacing used in practice. Option D is incorrect because it is a greater spacing than is required.