The correct answer is A. 90°.
When a cohesive soil specimen is subjected to a vertical compressive load, the cracks will form perpendicular to the direction of the applied load. This is because the soil particles are held together by cohesive forces, which are strongest when the particles are in contact with each other. When the soil is subjected to a vertical load, the particles are pushed together, which increases the cohesive forces between them. This causes the soil to become more rigid and less likely to deform. The cracks that form are perpendicular to the direction of the applied load because this is the orientation that minimizes the strain on the soil particles.
Option B is incorrect because the cracks would not form at a 45° angle to the horizontal. Option C is incorrect because the cracks would not form at a 22.5° angle to the horizontal. Option D is incorrect because the cracks would not form at a 0° angle to the horizontal.