The correct answer is A. 0.33.
The ratio of direct tensile strength to flexural strength is typically around 0.33. This means that a material that has a tensile strength of 100 MPa would have a flexural strength of around 33 MPa.
There are a few reasons why this ratio is typically so low. First, when a material is subjected to tensile stress, the entire cross-section of the material is in tension. However, when a material is subjected to flexural stress, only the top and bottom fibers of the material are in tension, while the middle fibers are in compression. This means that the material is not as efficient at resisting flexural stress as it is at resisting tensile stress.
Second, when a material is subjected to tensile stress, the material will tend to elongate. This elongation will cause the material to become weaker, as the bonds between the atoms in the material will be stretched. However, when a material is subjected to flexural stress, the material will tend to bend. This bending will not cause the material to elongate as much, and so the material will not become as weak.
Finally, it is important to note that the ratio of direct tensile strength to flexural strength can vary depending on the material. For example, concrete has a much lower ratio of direct tensile strength to flexural strength than steel. This is because concrete is a brittle material, and so it is not as good at resisting tensile stress as it is at resisting flexural stress.