The difference of two means in case of small samples is tested by the formula

A. $${\text{t}} = \frac{{{{\overline {\text{X}} }_1} - {{\overline {\text{X}} }_2}}}{{\text{S}}}\sqrt {\frac{{{{\text{n}}_1}{{\text{n}}_2}}}{{{{\text{n}}_1} + {{\text{n}}_2}}}} $$

B. $${\text{t}} = \frac{{{{\overline {\text{X}} }_1} - {{\overline {\text{X}} }_2}}}{{\text{S}}}$$

C. $${\text{t}} = \sqrt {\frac{{{{\text{n}}_1}{{\text{n}}_2}}}{{{{\text{n}}_1} + {{\text{n}}_2}}}} $$

D. $${\text{t}} = \frac{{{{\overline {\text{X}} }_1} - {{\overline {\text{X}} }_2}}}{{\text{S}}}\sqrt {\frac{{{{\text{n}}_1} - {{\text{n}}_2}}}{{{{\text{n}}_1}{{\text{n}}_2}}}} $$

Answer: Option B