Which of the following could lead to an engine not starting due to fuel issues?

The situation where an engine fails to start due to fuel issues is directly related to the availability of fuel. An empty fuel tank means that there is no fuel available for the engine to ignite, which is a fundamental requirement for any internal combustion engine to operate. When the fuel tank is empty, it simply does not provide the necessary fuel that is needed to mix with air for ignition.

While the other options may affect engine performance or operation in different ways, they do not directly relate to the availability of fuel in the system. For example, a faulty alternator can lead to electrical issues or battery problems, a blocked exhaust system can cause back pressure and hinder engine performance, and cold weather can affect fuel viscosity or starting conditions but does not eliminate fuel availability entirely. Therefore, when considering fuel issues specifically, an empty fuel tank is the clear and direct cause of an engine not starting.