Which of the following policies is primarily based on a named peril basis?

The correct choice, which is the bailee's customer policy, primarily operates on a named peril basis because it specifically covers losses caused by certain named risks while the property is in the care of the bailee. This type of policy highlights the importance of clearly defined perils such as theft, fire, or other specified causes of loss, ensuring that both the customer and the bailee have a clear understanding of what risks are covered.

In contrast, other policies may have broader or different coverage principles. For instance, an annual transit policy typically provides all-risk coverage, which is not limited to named perils. Motor truck cargo coverage often provides more comprehensive coverage rather than limiting it to named risks, and an open cargo policy generally covers risks on an all-risk basis rather than specifying individual named perils. Each of these options reflects a different approach to coverage, with the bailee's customer policy being distinct for its reliance on a specified list of covered perils.