Final answer:
The goniometric measurement of cervical lateral flexion uses the external occipital protuberance, C7 spinous process, and the horizontal axis of the goniometer as landmarks.
Step-by-step explanation:
The landmarks used to measure cervical lateral flexion are the external occipital protuberance, the C7 spinous process, and the horizontal axis of the goniometer. The external occipital protuberance is the bony bump on the back of the head; the C7 spinous process is a prominent protrusion at the base of the neck, which is a part of the seventh cervical vertebra; and the horizontal axis of the goniometer is the pivot point around which the device's arms rotate. Therefore, the correct answer to the question 'Which of the following landmarks are used to measure cervical lateral flexion?' is option a), as these landmarks provide the reference points required for accurately measuring the range of motion during lateral flexion of the cervical spine.