What does cargo capacity for most airports rely upon?

The correct answer reflects the understanding that cargo capacity at airports is significantly influenced by the volume of domestic passenger traffic. When airports experience high levels of passenger traffic, they typically have better infrastructure, such as additional cargo handling facilities and more efficient logistical operations to support cargo movement. This passenger traffic can also lead to increased availability of cargo space on passenger flights, which is often a common method of transporting air cargo.

High domestic passenger volumes can result in greater economic activity, which necessitates more cargo transport capabilities to support business and trade. Additionally, passenger flights often carry cargo, and more frequent flights due to higher passenger demand can directly benefit cargo shipments, allowing for faster and more reliable transport.

While the other options like weight, type of cargo, and distance of the cargo flight also play roles in cargo logistics, they do not directly determine the overall cargo capacity at airports the way that passenger volume does. These factors can influence specific shipments but are secondary to the broader operational capacity that passenger demands create.