Which soil type has the highest water-holding capacity?  

Clay soil has the highest water-holding capacity among the soil types listed.

This is because clay particles are very small and have a large surface area relative to their volume. This allows them to hold onto water molecules more tightly than other types of soil particles, such as sand or silt.

However, it's worth noting that soil water holding capacity is affected by various factors, including soil structure, organic matter content, and the presence of other soil components like rocks and gravel. So, the water holding capacity of any particular soil type may vary depending on these factors.