**Core Concept:** The shape of the arterial pulse is influenced by the properties of the arterial wall, the blood volume, and the blood pressure waveform. The arterial pulse is a manifestation of the systolic and diastolic pressure changes in the arterial system.

**Why the Correct Answer is Right:** The correct answer, C, is based on the fact that the arterial pulse shape is primarily influenced by the elasticity of the arterial wall. Elastic arteries, such as those in the upper body, tend to have a prominent pulse waveform with a rapid onset, a prolonged systolic duration, and a high pulse pressure. This is because the arterial wall can rapidly compress and expand, allowing for a significant change in volume during each heartbeat.

**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because the diameter of the artery does not significantly affect the pulse shape. The diameter changes during systole and diastole, but these changes are relatively minor compared to the changes in arterial wall compliance and blood pressure.
B. This option is incorrect because the blood volume does not directly determine the shape of the pulse waveform. While blood volume influences the overall amplitude of the pulse, the pulse shape is primarily determined by the arterial wall properties.
D. This option is incorrect because the blood pressure waveform does influence the pulse amplitude, but it does not directly determine the pulse shape. The pulse shape is determined by the arterial wall properties, specifically elasticity.

**Clinical Pearl:** The pulse shape can provide clues about the underlying cardiovascular health of a patient. For example, a slow onset and prolonged systolic duration may indicate arterial stiffness (e.g., in hypertension or ageing), while a rapid onset and short systolic duration suggest a compliant arterial wall (e.g., in young adults). A high pulse pressure represents increased arterial stiffness and is associated with cardiovascular disease risk.

**Correct Answer:** C. Arterial wall elasticity