Answer the following question given this paragraph: The enzyme pepsin works only in the presence of acid. A strong acid is secreted into the stomach. It provides the acid that pepsin needs. You will learn about acids in the next chapter, "Chemistry of Solutions. " Vinegar and lemon juice are two common acids. Q: The enzyme pepsin works only in the presence of what? Choices: - carbohydrates - sodium - oxygen - acid A:
A:
acid