Software Engineering Economy is an effective part of software engineering, which of the fol-lowing content is the research content of software engineering economy ( ) Ⅰ．Estimation of software development cost Ⅱ．Earn & Cost analysis of software development Ⅲ．Adjustment of software development progress

A．Ⅲ only

B．Ⅱ and Ⅲ

C．Ⅰ and Ⅱ

D．all