Final answer:
The best response from the nurse is to acknowledge the client's frustration and set boundaries about respectful communication, avoiding escalation and maintaining a professional relationship.
Step-by-step explanation:
The nurse's best response to a client who expresses anger by swearing after learning that their blood test has been canceled is, "I see that you are upset, but I feel uncomfortable when you swear at me." This approach acknowledges the client's emotions while setting boundaries regarding respectful communication. It's an example of therapeutic communication, where the nurse avoids escalating the situation and instead focuses on maintaining a professional and caring relationship with the client.