With regard to the basic rules to follow when developing a Project Network, which of the following statements is not correct?

An activity identification number must be greater than that of any activities that precede it An activity cannot begin until all preceding connected activities have been completed Each activity should have a unique identification number Looping is not allowed Networks flow typically from left to right Conditional activities are used when more than one path can be followed in a project, depending on the outcome of the activity Arrows on networks indicate precedence and flow and can cross over each other