The correct answer is A. effective size.
The effective size is a measure of the average particle size in a granular material. It is calculated by taking the geometric mean of the d10 and d60 particle sizes, where d10 is the particle size at which 10% of the particles are smaller and d60 is the particle size at which 60% of the particles are smaller.
The uniformity coefficient is a measure of the range of particle sizes in a granular material. It is calculated by dividing the d60 particle size by the d10 particle size. A high uniformity coefficient indicates a narrow range of particle sizes, while a low uniformity coefficient indicates a wide range of particle sizes.
The coefficient of curvature is a measure of the shape of particles in a granular material. It is calculated by taking the ratio of the d30 particle size to the d10 and d60 particle sizes. A high coefficient of curvature indicates that the particles are spherical, while a low coefficient of curvature indicates that the particles are elongated.
None of the above options are measures of particle size range.