The architecture design specifies the overall architecture and the placement of software and hardware that will be used. Architecture design is a very complex process that is often left to experienced architecture designers and consultants. The first step is to refine the （nonfunctional requirements） into more detailed requirements that are then employed to help select the architecture to be used and the software components to be placed on each device. In a （client-server architecture）, one also has to decide whether to use a two-tier, three-tier, or n-tier architecture. Then the requirements and the architecture design are used to develop the hardware and software specification. There are four primary types of nonfunctional requirements that can be important in designing the architecture. （Operational requirements） specify the operating environment（s） in which the system must perform and how those may change over time. （Performance requirements） focus on the nonfunctional requirements issues such as response time, capacity, and reliability. （Security requirements） are the abilities to protect the information system from disruption and data loss, whether caused by an intentional act. Cultural and political requirements are specific to the countries in which the system will be used.
系统架构设计是由资深架构师主导的复杂流程，核心是将高层需求细化为具体需求，以此完成架构选型、软硬件部署规划及规格制定。其中，客户端-服务器（C/S）架构是分布式系统的主流架构，可根据业务复杂度设计为两层、三层或多层架构，区别于客户端主导、服务器主导的单一架构模式。
非功能需求是架构设计的关键考量维度，核心包含四类：运行需求，明确系统的运行环境及环境的动态变化要求，保障系统场景适配性；性能需求，聚焦响应时间、系统容量、可靠性等核心指标，直接决定系统服务能力；安全需求，重点在于防御恶意攻击、避免数据泄露与系统中断，需与人身设备安全类需求明确区分；此外还有文化政治需求，需匹配系统部署地区的特定规则。另外要明确，功能需求侧重业务功能实现，非功能需求侧重系统质量属性，系统约束是必须遵守的外部限制，与非功能需求存在本质差异，维护性需求则属于非功能需求中关乎系统后期维护效率的类别。
本题考察的是系统架构设计中的非功能需求分类及其应用。
语境定位：原句为 “The first step is to refine the ____ into more detailed requirements that are then employed to help select the architecture to be used and the software components to be placed on each device.”。空前 first step is to refine the；空后 into more detailed requirements that are 是判断本空的关键。
答案判断：从语法看，这里需要名词或名词短语；从语义看，应填“非功能需求，描述性能、安全、可用性等质量约束”。因此应选 nonfunctional requirements。
选项辨析：
A. functional requirements：描述系统应具备的业务功能，与架构性能无关，错误。
B. nonfunctional requirements：描述系统的质量属性，如性能、可用性、安全性等，本题明确指出是将其细化为详细需求，因此，符合语境。
C. system constraint：指系统必须遵守的限制条件，不等同于本题描述的非功能需求，错误。
D. system operational environment：指运行环境，不是总类，错误。
因此，选项 B 正确。