Given the task definition and input, reply with output. 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 raise ph in pool [title] Test the pool water's ph level with test strips. [step] Get ph testing strips at your local pool store, big-box store, or order them online. Follow the product's instructions, which are typically dipping the strip into the water and checking its color against the range listed on the product. <sep> (A) Dissolve or screw the strip into the pool water and use it to test the water for ph. [substeps] Consult your local professional pool store or search online to determine if the test strips will clearly show your ph. (B) [substeps] Test samples and readings on the test strips. Some tests touch on ph, but others don't. (C) [substeps] Consult your product's instructions for the ph level you should test. Phosphate-free, ph under 16 percent is the ph needed to raise ph at the pool, while ph below 19 percent is the ph required to go swimming. (D) [substeps] Some ph test kits require you to fill a small tube with pool water and add drops which change color based on the ph. [title] Check the chemical levels one to two times per week.
D