The purpose of the requirements definition

问题：

The purpose of the requirements definition phase is to produce a clear, complete, consistent, and testable (87) of the technical requirements for the software product.
During the requirements definition phase, the requirements definition team uses an iterative process to expand a broad statement of the system requirements into a complete and detailed specification of each function that the software must perform and each (88) that it must meet. The starting point is usually a set of high-level requirements from the (89) that describe the project or problem.
In either case, the requirements definition team formulates an overall concept for the system and the defines (90) showing how the system will be operated, publishes the system and operation concept documents, and conducts a system concept review (SCR).
Following the SCR, the team derives (91) requirements for the system from the highlevel requirements and the system operations concept. Using structured or object-oriented analysis,the team specifies the software functions and algorithms needed to satisfy each detailed requirements.

A. function B. definition
C. specificationD. statement