You are in charge of a large software development project. As a part of the project schedule $-$ it was planned to complete two core components by the end of October. You are now in August and you realize that the project is falling behind schedule. You do a quick review and decide that the schedule can be met by adding additional staff to the activities on the critical path. This is an example of :

a$.$ Crashing

b$.$ Scope Creep

c$.$ Resource Levelling

d$.$ Fast Tracking