The correct answer is A. 10.
A simply supported beam is a beam that is supported at both ends. The stiffness of a beam is its ability to resist deformation under load. The ratio of the span of a beam to its overall depth is a measure of its stiffness. A higher ratio means that the beam is stiffer.
For normal cases, the stiffness of a simply supported beam is satisfied if the ratio of its span to its overall depth does not exceed 10. This means that if the span of a beam is 10 meters, its overall depth should not be less than 1 meter.
If the ratio of the span to the overall depth is greater than 10, the beam will be too flexible and will not be able to support the load without deforming significantly.
Options B, C, and D are incorrect because they are greater than 10.