Final answer:
The description of the ultrasound beam cannot be confirmed from the provided context; therefore, the most conservative answer, without evidence of focusing or steering, would be 'unfocused, no steering'.
Step-by-step explanation:
To describe the ultrasound beam based on the provided context, we note that the beam is created by having multiple ultrasound sources in the probe's head, which are phased to interfere constructively in a given, adjustable direction. This phasing capability allows the beam to be steered to the right or left, and the constructive interference can create a focus. Given that no additional information indicates explicit focusing or steering in a particular direction, we cannot confirm whether the beam is focused or steered to the right or left from the context provided alone. Therefore, without an accompanying figure or additional details, none of the provided phrases b, c, or d can be verified as accurately describing the ultrasound beam. Without evidence of focusing or steering, the most conservative choice would be.