Final answer:
The parameters in an ultrasound system can be established, while some must be changed by the sonographer. The ability to change parameters is important for optimizing image quality.
Step-by-step explanation:
The correct answer is B) can; must.
Some parameters can be established by the ultrasound system or the sonographer, while some parameters must be changed. For example, the ultrasound system may have preset parameters such as frequency and depth, but the sonographer must be able to adjust the settings to optimize the image quality for different types of examinations.
Being able to change parameters is important because it allows the sonographer to tailor the ultrasound examination to the specific needs of the patient and to account for differences in tissue characteristics and imaging requirements.