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