If Two Random Samples of Sizes N₁ and N₂ Are $\bar { X } _ { 1 } - \bar { X } _ { 2 }$

If two random samples of sizes n₁ and n₂ are selected independently from two non-normally distributed populations, then the sampling distribution of the sample mean difference, $\bar { X } _ { 1 } - \bar { X } _ { 2 }$ , is

A) always non-normal
B) always normal
C) approximately normal only if n₁ and n₂ are both larger than or equal to 30
D) approximately normal regardless of n₁ and n₂