TOPIC: Legal requirement an assumption or EEF

A particular project in the domain of civil construction requires that every on-site worker be insured. Which of the following inputs BEST conveys this requirement to the Estimate Costs process so that the insurance cost is estimated and subsequently budgeted:
a. Enterprise Environmental Factor
b. Organizational Process Assets
c. Project Scope Statement
d. Project Management Plan
The correct answer is Project scope statement. To me it sounds like an EEF. Does anybody know why?

Please state the origin of the question; where did this come from?

The Project Scope Statement details all the project work needed to deliver the end product service or result Insurance would be a project requirement for this situation based on the location, zone etc. It would not necessarily be a corporate EEF.