Which writing type explains how something works and discusses its component parts?

The choice that best describes a writing type explaining how something works and discussing its component parts is functional or technical writing. This genre of writing is specifically designed to convey detailed information about a process, product, or topic. It focuses on clarity, precision, and structure, often using diagrams, step-by-step instructions, or lists to enhance the reader's understanding.

Functional or technical writing is commonly found in manuals, user guides, and documentation where the primary goal is to inform or instruct the reader on how to use, operate, or understand something effectively. The emphasis on the mechanical aspects and the description of each component aligns perfectly with the requirement of discussing how something works.

In contrast, expository writing also aims to explain ideas or concepts, but it may not always delve into the mechanics or component parts in the detailed manner that functional or technical writing does. Stream of consciousness is a narrative style that captures thoughts and feelings in a flow, lacking the structured explanation of components. Cause and effect writing focuses on the relationship between events or concepts rather than the functional operation of something. Thus, the specific emphasis on components and operation makes functional or technical writing the correct choice here.