According to the textbook context: (a) A region with high annual rainfall has ample water resources and no mention of other scarcity factors, so it does not suffer from water scarcity. (b) A region with high rainfall but large population suffers from water scarcity because 'water scarcity may be an outcome of large and growing population and consequent greater demands for water.' (c) A region with high rainfall but highly polluted water suffers from water scarcity because 'even if there is ample water to meet the needs of the people, much of it may be polluted... thus, making it hazardous for human use.' (d) A region with low rainfall and low population does not suffer from water scarcity because the low population means demand matches the limited supply, and scarcity is caused by 'over-exploitation, excessive use and unequal access to water.'