Two Samples of Sizes 22 and 18 Are Independently Drawn $\begin{array}{|l|l|}\hline A&\text { 39}\\\hline B&\text {40 }\\\hline C&\text {38 }\\\hline D&\text { 41}\\\hline\end{array}$

Two samples of sizes 22 and 18 are independently drawn from two normal populations, where the unknown population variances are assumed to be equal. The number of degrees of freedom of the equal-variances t-test statistic is: $\begin{array}{|l|l|}\hline A&\text { 39}\\\hline B&\text {40 }\\\hline C&\text {38 }\\\hline D&\text { 41}\\\hline\end{array}$