You ______ the cat out for a walk.[ ]

A. needn't to take

B. don't need take

C. don't need to take

D. needn't taking

离心式自动生化分析仪加样时，转头中的空槽也必须用相同方法加入蒸馏水是为了

A．提高分析精密

B．减少污染

C．保持平衡

D．校正零点

E．做空白对照