Answer: D

Reasoning: The deep cervical fascia is conventionally divided into investing (superficial), pre-tracheal (middle), and pre-vertebral (deepest) layers; the carotid sheath is a specialization that lies between these layers. Therefore, the prevertebral fascia forms the deepest layer of cervical fascia [Miyake et al., 2011, PMID 21647961; Gavid et al., 2018, PMID 29380103].