Five Year Plans

Step 1: Understanding the question.
The question is asking about the initiation of the Mountainous Area Development Program, which began in the Fifth Five-Year Plan of India.
Step 2: Analyzing the options.
(A) तीसरी: This is incorrect, as the program was introduced in the Fifth Plan.
(B) चौथी: This is incorrect. The program started in the Fifth Five-Year Plan.
(C) पांचवीं: Correct — The program started during the Fifth Five-Year Plan to address the development needs of mountainous regions.
(D) छठी: This is incorrect, as it started in the Fifth Plan, not the Sixth.
Step 3: Conclusion.
The correct answer is (C) पांचवीं, as the program was launched during the Fifth Five-Year Plan.