小儿肠粘膜肌层发育差，肠系膜柔软而长，升结肠与后壁固定差，易发生___和___。

The purpose of the requirements definition phase is to produce a clear, complete，consistent, and testable______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______that it must meet. The starting point is usually a set of high-level requirements from the______that describe the project or problem.
In either case, the requirements definition team formulates an overall concept for the system and then defines______showing how the system win be operated, publishes the system and operations concept document, and conducts asystem concept review(SCR).
Following the SCR，the team derives______requirements for the system from the operations concept. Using structured or object-oriented analysis, the team specifies the software functions and algorithms needed to satisfy each detailedrequirement.

A．rules
B．principles
C．scenarios
D．scenes