You are a project manager on a $$15,000,000$ software development project. While working with your project team to develop a schedule network diagram, your data architects suggest that quality could be improved if the data model is approved by senior management before moving on to the design phase. They support this suggestion with an article from a leading software development journal. This type of input is called a$($n$)$:Select one:a$.$ Discretionary dependency b$.$ Mandatory dependencyO c$.$ Heuristic d$.$ External dependency