单项选择题

A.40%甲醛10ml,0.01mol/L蒸馏水90ml
B.40%甲醛10ml,0.01mol/LpH7.4的PBS90ml
C.40%甲醛10ml,0.01mol/LpH7.4的PBS100ml
D.10%甲醛10ml,0.01mol/LpH7.4的PBS90ml
E.10%甲醛10ml,0.01mol/L蒸馏水90ml