The software architecture of a program or computing system is the structure or structures of the system, which comprise software （1）, the externally （2）properties of those components, and the relationships between them. The architecture is not the operational software. Rather, it is a （3） that enables a software engineer to: analyze the （4）of the design in meeting its stated requirements, consider architectural alternatives at a stage when making design changes is still relatively easy, and reduce the（5） associated with the construction of the software.
（2）是（）
A.visible
B.reliable
C.secure
D.robust