An architectural style defines as a family of such systems in terms of a （1）of structural organization. More specifically, an architectural style defines a vocabulary of（2） and connector types, and a set of （3） on how they can be combined. For many styles there may also exist one or more （4） that specify how to determine a system’s overall properties from the properties of its parts. Many of architectural styles have been developed over the years.

The best-known examples of （5） architectures are programs written in the Unix shell.

（4）是（）

A. semantic models

B. weak entities

C. data schemas

D. business models

为什么要对焦炉煤气进行初步冷却？