2 paragraph essay

 Based on the information in the article, and the lessons learned in the article,

 (a) what in your opinion are the key challenges for estimation that big-dig faced? 

 (b) Reflect on whether estimation is a one time phenomenon, or an iterative process?  Why ? - I especially would like to know why? 

(c) What can you do as a project manager in improving cost estimates in these projects. 

Use your own word, not need citation or reference.

 Please write two paragraphs (essay type) on the key challenges with estimation in the project.