Final answer:
The landmarks used to measure cervical flexion are the external occipital protuberance, the C7 spinous process, and the horizontal axis of the goniometer.
Step-by-step explanation:
To measure cervical flexion using a goniometer, specific anatomical landmarks must be identified and utilized. The correct landmarks for assessing cervical flexion are a) the external occipital protuberance, the C7 spinous process, and the horizontal axis of the goniometer. The external occipital protuberance is a palpable bony prominence located at the posterior base of the skull. The C7 spinous process, also referred to as the vertebra prominens, can be felt as the most prominent structure when running a finger along the midline of the back of the neck at the base. It represents the start of the thoracic spine and serves as a key reference point. Lastly, the horizontal axis, or fulcrum, of the goniometer is positioned at the side of the head to help measure the degree of flexion accurately.