A Study Randomly Assigned 60 Adults Diagnosed with Metabolic Syndrome

A study randomly assigned 60 adults diagnosed with metabolic syndrome to two groups, each containing 30 patients. One group was given daily tablets containing the Chinese herbal supplement Yiqi Huaju Qingli, while the other group was given daily placebo tablets. All 60 patients maintained their standard medical treatment throughout the 12 weeks of the study. Urinary microalbumin is a key factor in metabolic syndrome and an early sign of diabetic nephropathy. Urinary microalbumin (in mg/l) was assessed for all participants at the beginning and at the end of the study. Here are the published findings, expressed as "mean (standard deviation) ":
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$$\begin{array} { | l | l | l | } \hline & \text { Herbal Supplement } & \text { Placebo } \\\hline \text { Start of study } & 101.58 ( 75.39 ) & 98.50 ( 66.92 ) \\\hline \text { End of study } & 47.11 ( 27.85 ) & 78.87 ( 60.65 ) \\\hline\end{array}$$ Given that the degrees of freedom for the appropriate t procedure is roughly 40, what is a 95% confidence interval for ?_Herbal¯?_Placebo at the end of the study?

A) -31.76 ± 12.31 mg/l
B) -31.76 ± 16.40 mg/l
C) -31.76 ± 24.61 mg/l
D) -31.76 ± 49.22 mg/l