To Construct an Interval Estimate for the Difference Between the Means

To construct an interval estimate for the difference between the means of two populations when the standard deviations of the two populations are unknown and it can be assumed the two populations have equal variances, we must use a t distribution with (let n₁ be the size of sample 1 and n₂ the size of sample 2)

A) (n₁ + n₂) degrees of freedom
B) (n₁ + n₂ - 1) degrees of freedom
C) (n₁ + n₂ - 2) degrees of freedom
D) n₁ - n₂ + 2