Alack of clean drinking water is the leading cause of in the poorest parts of the world. a. inflation b. drought c. unemployment d. disease

The answer is D:Disease

Drought isn't caused by the lack of clean water, inflation? of what? unemployment? lack of clean water has very little to do with employment of individuals.

Disease, by far. It is one matter having no water, and another having no clean drinking water. When we use the definition clean, we mean potable, or free from microbes that would cause disease. Places like Yemen for example lack potable water, and are now experiencing a massive epidemic of a waterborne illness called Cholera.