The Rational Unified Process (RUP) is a software engineering process, which captures many of best practices in modern software development. The notions of （） and scenarios have been proven to be an excellent way to capture function requirements. RUP can be described in two dimensions – time and content. In the time dimension, the software lifecycle is broken into cycles. Each cycle is divided into four consecutive （） which is concluded with a well-defined （） and can be further broken down into （） – acomplete development loop resulting in a release of an executable product, a subset of the final product under development, which grows incrementally to become the final system. The content structure refers to the disciplines, which group （） logically by nature.

and can be further broken down into （） – acomplete development loop resulting in a release of an executable product.

A．rounds

B．loops

C．iterations

D．circularities

动机机油压力过低的原因有哪些？