In Practice,we Typically Know the Values of _____,But We Do

Multiple Choice

In practice,we typically know the values of _____,but we do not know the values of _____.

A) n₁ and n₂;ó₁² and ó₂²
B) the sample means;n₁ and n₂
C) n₁ and n₂;the sample means
D) ó₁² and ó₂²;n₁ and n₂