Final answer:
The investing fascia is part of the deep cervical fascia, and therefore they are the same structure.
Step-by-step explanation:
The relationship between the investing fascia and the deep cervical fascia is that the investing fascia is a layer of the deep cervical fascia itself. Specifically, the investing fascia is one of the components that make up the deep cervical fascia, which encloses muscles, glands, and other structures in the neck. Therefore, the correct answer to the question is that they are the same structure, as the investing fascia is part of the deep cervical fascia.