Which grading type is characterized by particle sizes that lack diversity?

The choice of uniformly graded is correct because this grading type comprises particles that are similar in size, leading to a lack of diversity within the sample. In uniformly graded materials, the particle sizes are close to one another, which means that there is minimal variation in size. This uniformity can affect the material's overall behavior, such as its compaction characteristics and drainage properties.

In contrast, well-graded materials contain a range of particle sizes, allowing for better packing and stability due to the presence of smaller particles filling the voids between larger particles. Medium graded materials have a balance of different particle sizes but still exhibit some diversity. Gap graded materials consist of missing sizes in a particle size distribution, meaning they have a mix of large and small particles but lack mid-sized ones. Therefore, uniformly graded is the best choice as it distinctly emphasizes the lack of diversity in particle size.