For the formula $t=\frac{\mu_1-\mu_2}{\sqrt{\frac{S_1^2}{n_1}+\frac{S^2_2}{n_2}}}$ consider of the following statements :

A. $\mu_1$ and $\mu_2$ are sample mean and population mean respectively.

B. $n_1$ and $n_2$ are sample sizes of two samples from same population.

C. $S_1$ and $S_2$ are sample means of two samples from same population.

D. $S_1$ and $S_2$ standard error of two samples from same population.

E. $n_1$ is the sample size and $n_2$ is the population size.

Choose the correct answer fro the options given below :

B and D only