"Unknown Unknowns" Are Unexpected Events Which Can Occur When the Project

Multiple Choice

"Unknown unknowns" are unexpected events which can occur when the project is underway.All of the following accurately describe an implication associated with unknown unknowns EXCEPT: 

A)  They are usually discovered during risk identification 
B)  They need to be covered in the project budget. 
C)  They usually require the use of management reserve. 
D)  They usually cause an increase in cost and / or schedule.