You believe the project team will only contribute six hours, but you haven’t proven this to be true. The project team could work more, or less, than six hours per day. 2 is not a valid choice, because if it’s true that the labor union will only allow six hours of work, then it’d be a constraint. 3 is incorrect because if you have historical information to base your time estimate on then it’s factual rather than an assumption. 4 is incorrect because if you know the building inspector will be on-site for two hours each day this is a constraint.