**Core Concept**
The International Drinking Water Supply and Sanitation Decade Programme was a global initiative aimed at improving access to safe drinking water and sanitation facilities. This programme was a collaborative effort between the United Nations and its member states to address the pressing issue of water-borne diseases and related health problems.

**Why the Correct Answer is Right**
The International Drinking Water Supply and Sanitation Decade Programme was launched in 1981 to address the significant gap in access to safe drinking water and sanitation facilities worldwide. The programme's primary goal was to improve the health and well-being of communities by providing them with access to safe drinking water and proper sanitation facilities. The programme focused on increasing access to water supply systems, improving sanitation infrastructure, and promoting hygiene practices to prevent water-borne diseases.

**Why Each Wrong Option is Incorrect**
**Option A:** 1975 is incorrect because it predates the actual launch of the programme, which was a response to the growing global concern about the need for improved water and sanitation facilities.
**Option B:** 1978 is incorrect because it is the year the United Nations General Assembly adopted the resolution that led to the launch of the programme, but it is not the actual launch year.
**Option C:** 1984 is incorrect because it is a year after the programme's launch and not relevant to the initial launch date.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the International Drinking Water Supply and Sanitation Decade Programme was a key initiative in addressing the global water crisis, and its impact is still felt today in the form of improved access to safe drinking water and sanitation facilities in many parts of the world.

**✓ Correct Answer: D. 1981**