The Following MINITAB Output Display Presents the Results of a Hypothesis

The following MINITAB output display presents the results of a hypothesis test for the difference $\mu _ { 1 } - \mu _ { 2 }$ between two population means. Difference $= \mathrm { mu } ( \mathrm { X } 1 ) - \mathrm { mu } ( \mathrm { X } 2 )$
Estimate for difference: $- 10.373$
$95 \%$ CI for difference: $( - 34.072,13.326 )$
$\mathrm { T } -$ Test of difference $= 0 ($ vs not $= ) : \quad$ T-Value $= - 0.857889$
$$\text { P-Value } = 1.593507 \quad \text { DF } = 13$$ How many degrees of freedom are there for the test statistic?

A) 10.373
B) 12
C) 1.593507
D) 13