参考答案：A

解析：

Daily weight shows trends and can assist medical management by indicating if interventions and medications are effective. Laboratory data are objective data that indicate whether electrolyte levels are within normal limits for the client with fluid balance problems. However, if a client is dehydrated, some laboratory data can show false elevations. Intake and output is extremely important, but matching the two is difficult because fluid is also lost through breathing, perspiration, stool, and surgical tubes. Vital signs may or may not be helpful because heart rate and blood pressure can be elevated by either depletion or excess of fluids in some situations.