Fact 1: Cells secrete acids and bases to maintain the proper pH for enzymes to work. Fact 2: An enzyme is a biological catalyst . Given the two facts above, catalysts require proper what to work?

(a). DNA.
(b). pH.
(c). pan.
(d). RNA.
(e). elevation.
(f). time of day.
(g). gas.
(h). humidity.
Answer:
(b).