Which of the following is true regarding the shape of the sampling distribution of the statistic x bar 1 minus x bar 2 for independent and random samples? PLEASE EXPLAIN

A) The shape is a t-distribution with df = (n1+n2-2) with unknown population variances and sample sizes of < 30 assuming normally distributed populations

B) The shape is normal when the samples are random and independent

C) The shape is normal if n1p1, n1(1-p1) and n2p2, n2(1-p2) are all at least 15

D) The shape is normal for unknown population variances and sample sizes of < 30