A Researcher Wants to Determine Whether the Means of Two $\quad$

A researcher wants to determine whether the means of two independent populations are the same.She has two independent random samples, one from each population, shown in the following table: $\quad$ $\quad$ $\quad$ $\quad$ Sample I $\quad$ $\quad$ $\quad$ $\quad$ $\quad$ $\quad$ $\quad$ Sample II
$\begin{array}{llll|lllll}\hline 11.5 & 15.7 & 22.8 & 22.5 & 12.6 & 13.8 & 17.5 & 10.7 & 13.5 \\12.4 & 25.3 & 16.1 & 25.1 & 14.8 & 11.8 & 14.7 & 10.8 & 12.7\end{array}$

She uses the Mann-Whitney U test and a significance level of 0.05.Then $\mu$ _U is ______.

A) 4.5
B) 9
C) 31.5
D) 40
E) 63