Explanation:

- The Integrated Development of Small and Medium Towns (IDSMT) is a centrally sponsored scheme aimed at improving infrastructure and services in small and medium-sized towns.

- Option 1: 1978-79

- This option reflects one of the early years when plans for development in urban areas were considered.

- However, it is not the correct launch year for IDSMT.

- Option 2: 1975-76

- This year includes events of broader economic development plans.

- It is not related to the start of IDSMT.

- Option 3: 1980-81

- This period involved several urban development schemes.

- Nonetheless, it isn’t when IDSMT began.

- Option 4: 1979-80

- This is the correct year when the IDSMT was initiated, focusing on uplifting infrastructure in smaller urban areas.

- This is the correct answer.