Final answer:
A dialysis technician can check a patient's blood pressure before starting dialysis, which is within their scope of practice under the supervision of a registered nurse.
Step-by-step explanation:
Among the options provided, the most appropriate nursing action that can be delegated to a dialysis technician is B. Check blood pressure before starting dialysis. Dialysis technicians are trained to review patient history, assist with the dialysis treatment process, and take and report a patient's vital signs under the direct supervision of a registered nurse. Tasks such as teaching patients about fluid restrictions, assessing causes for weight changes, and determining ultrafiltration rates are within the scope of practice for a registered nurse and typically require a higher level of clinical judgment and expertise.