Which condition might increase the risk of nozzle drip at shut down?

The presence of air in the line can lead to increased risk of nozzle drip at shutdown because it disrupts the fuel flow dynamics. When air becomes trapped in the fuel line, it can create pressure fluctuations that cause the nozzle to fail to properly seal when the flow of fuel is interrupted. This may result in residual fuel continuing to drip from the nozzle after the shut-off has occurred, rather than properly stopping the flow.

In contrast, high ambient temperature could potentially alter fuel viscosity but isn't a direct cause of nozzle dripping after shutdown. Low fuel level might influence pressure but doesn't directly create conditions for dripping as effectively as air in the line. An overfilled tank can introduce issues such as spillage, but it is less about air in the lines affecting the nozzle's sealing capability when shutting down. Therefore, having air in the line is the most relevant factor, as it directly affects the functionality and sealing of the nozzle during and after operation.