Help with a biology Question please!!! =]]?

Question

A student sets up an experiment involving a color reaction in which the spectrophotometer will be used to monitor the extent of the reaction. Liquid A pollen is combined with reagent B, which the student provides. The product of the reaction [P] is treated with reagent C to produce a colored complex.

What is the appropriate blank for zeroing the spectophotometer prior to making readings?

[A] P and C in equal volumes

[B] comparable volumes of C and B and water to replace A

[C] comparable volumes of A,B,P, and C

[D] water

[E] water and comarable volumes of A and B

Answer 1

[D] water