Below are the choices:
A. Many developing nations lack access to clean water; this can harm human health.
B. Clean water is never available in developing nations, so human health is always a major issue there.
C. Human health does not depend on clean water; health issues in developing nations are not related to water.
D. Contaminated water and human health is not a problem in developing nations, but it is a problem in developed nations.
The answer is A.