If a cargo of kerosene were considered "too lean" to explode, then it must be which of the following?

Correct Answer: Option D — below the "explosive range"

The explosive range exists between the Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL). If a mixture is too lean, the concentration of fuel vapor is below the LEL, meaning there is insufficient fuel to support combustion. It is below the explosive range, rendering the atmosphere non-flammable.