What is a fourth-party logistics provider?

A、a company that ensures that various third-party logistics companies are working toward the relevant supply chain goals and objectives
B、a third-party logistics provider that has achieved ISO 9000 certification
C、a logistics intermediary that specializes in one logistics activity, such as warehousing or transportation
D、a third-party logistics provider that specializes in two or more logistics activities, such as warehousing and transportation