Detailed Instructions: 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".
Q: [header] How to add potassium to an organic garden [title] Mix in muriate of potash or sulfate of potash. [step] Muriate of potash, or potassium chloride, and sulfate of potash, or potassium sulfate, are natural minerals. Muriate of potash tends to be cheaper, but the chlorine it contains can hurt the helpful microbes living in your garden's soil. <sep> (A) Gently mix these two together first, then add the zinc sulfate. [substeps] Zinc sulfate is readily available online, or in desalination solutions. (B) [substeps] You can substitute sodium thiamine (ipsin) or baking soda for sulfate because it is the most acidic fertilizer. Sodium thiamine is a common fertilizer in agricultural and organic gardens. (C) Sulfate of potash is safer, but it's a bit more expensive. [substeps] Check your product's label for specific instructions on how much to add per square foot or meter. (D) [substeps] There are many ways to add potassium to soil: you could use the most common method. You could sift the potassium into an empty feed colander and cool it before dropping it off.
A:
C