Option C: Approach higher authority to reconsider the leave application._
     ● Step 1: _Assess the Situation_: You are handling a priority project and have been meeting all deadlines, which indicates your commitment and responsibility towards your work. However, you also have a personal need to take leave.  
     ● Step 2: _Evaluate the Options_:  
       ● Option A: Proceeding on leave without sanction is unprofessional and could lead to disciplinary action. It shows a lack of respect for the authority and the project's needs.  
       ● Option B: Pretending to be sick is dishonest and could damage your reputation and trustworthiness within the organization.  
       ● Option D: Telling the boss that their decision is unjustified might come across as confrontational and could strain your relationship with your boss.  
       ● Option C: Approaching a higher authority is a professional way to seek reconsideration. It shows that you respect the chain of command and are seeking a resolution through appropriate channels.  
     ● Step 3: _Choose the Best Option_: Given the circumstances, Option C is the most appropriate choice. It allows you to express your need for leave while maintaining professionalism and respect for the organizational hierarchy.