Final answer:
Trace protein in the urine can indicate improvement in a client with mild preeclampsia, as protein levels are decreasing and possibly returning to normal, whereas elevated blood pressure and BUN values are concerning and require monitoring.
Step-by-step explanation:
A sign that indicates improvement in the client's condition with mild preeclampsia would be a decrease in the severity of symptoms and stabilization of vital signs such as blood pressure. Regarding the options provided, the presence of trace protein in the urine could be seen as a sign of improvement, as mild preeclampsia often presents with proteinuria (protein in the urine). Severe preeclampsia might show a significant amount of protein, so a reduction to trace levels can be a positive indicator.
However, a blood pressure of 148/94 mm Hg is still considered high and indicative of hypertension, which requires monitoring and management. Also, a Blood Urea Nitrogen (BUN) level of 40 mg/dL (14.2 mmol/L) is elevated, suggesting that kidney function may be compromised. High BUN levels can be a part of the renal impairment seen in severe cases of preeclampsia, so a decrease would be more indicative of improvement.
The most likely correct answer would be 'B.Trace protein in the urine' since it shows potential progression towards normalcy in kidney function as related to the client's preeclampsia condition.