A.個體觀察值和樣本均數(shù)之差 B.個體觀察值和總體均數(shù)之差 C.個體觀察值和個體觀察值之差 D.樣本均數(shù)和樣本均數(shù)之差 E.樣本均數(shù)與總體均數(shù)之差