If t is the duration of an activity, t 1 is the latest finish possible moment of its preceding activity and t 2 is the earliest start possible moment, the independent float of the activity is

• A. ( t 1 - t 2 ) - t
• B. t - ( t 1 - t 2 )
• C. ( t 1 + t 2 ) - t
• D. t + ( t 1 - t 2 )