The correct answer is B) Low lube oil pressure. Low lube oil pressure is one of the primary safety mechanisms that will automatically shut down a diesel engine. This is because low lube oil pressure indicates a lack of proper lubrication, which can rapidly lead to engine damage and failure if not addressed. The engine's control system is designed to detect low lube oil pressure and initiate an automatic shutdown to prevent further damage. The other options are incorrect because they do not universally trigger an automatic shutdown. High jacket water pressure, high lube oil pressure, and excessive turbocharger speed may cause warnings or reduced engine performance, but they do not necessarily result in an automatic shutdown like low lube oil pressure does.