Final answer:
Black pipe is associated with iron pipe, which is coated with black material to prevent rust.
Step-by-step explanation:
The categories of pipe referenced in the question pertain to different materials used for plumbing. The term 'black pipe' is commonly associated with iron pipe because it is made of iron or steel and is coated with a layer of black zinc or iron oxide to prevent rusting. It is often used for gas lines and other industrial applications rather than for water delivery. Therefore, the answer to the question 'Which of the following categories of pipe is black pipe?' is A. iron pipe.