Which of the following is NOT one of the four phases of SDLC?

The correct answer is "Execution," as it is not recognized as one of the four phases of the Systems Development Life Cycle (SDLC). The four standard phases of SDLC typically include Planning, Design, Implementation, and Evaluation or Maintenance.

In the context of SDLC, planning involves defining the scope and objectives of the project and identifying resources needed. The design phase focuses on creating the specifications and architecture for the system, ensuring that all requirements and functionalities are planned out. Implementation is where the actual coding and deployment of the system occur, translating designs into a functioning system.

The concept of execution might refer to aspects of implementation or running the system, but it is not a designated phase within the formal structure of SDLC. Each phase has its specific focus and tasks that guide the development of software systems methodically and efficiently. Understanding the defined phases helps ensure clarity in project management and execution of software development tasks.