You will be given a definition of a task first, then some input of the task.
In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D".

[header] How to test for cyanuric acid [title] Make sure your state allows cyanuric acid. [step] Every state has different laws and different levels they allow, from 30 ppm as the maximum to 100 ppm as the maximum. It's essential you know what you are testing for, depending on your location. <sep> (A) [substeps] In oregon, the minimum required is a 30 ppm three times maximum. California requires an 80 ppm of cyanuric acid. (B) [title] Visit your state's plus = 0 data center. [step] The plus is 2, therefore, you are testing for cyanuric acid. (C) [title] Understand the benefit of cyanuric acid. [step] In the right amounts, cyanuric acid protects the chlorine in a pool from ultraviolet sunlight, thereby reducing the amount of chlorine lost over time. (D) [substeps] Add cyanuric acid to one gallon of water in a pool or bath. Adding it to a full liter of water is not advisable.
Output:
C