Answer

A

Explanation

The question is asking which of the given options - oil, salt, or mercury - threatens water resources. Water pollution is a significant environmental issue, and it can be caused by various pollutants. Among the options provided:1. Oil: Oil spills and leaks can cause significant water pollution. When oil enters water bodies, it can harm marine life, disrupt food chains, and contaminate drinking water sources. Oil forms a thick layer on the water surface, preventing oxygen from reaching aquatic organisms and blocking sunlight, which can affect photosynthetic organisms in the water.2. Salt: While salt can affect water quality, especially in freshwater systems, it is not typically classified as a pollutant that threatens water resources in the way that oil or mercury does. High salinity levels can be harmful to freshwater organisms, but salt is naturally present in many water bodies.3. Mercury: Mercury is a toxic heavy metal that can contaminate water bodies through industrial processes and waste disposal. It can accumulate in fish and shellfish, posing a risk to human health when these contaminated organisms are consumed. Mercury can disrupt the nervous system and cause other health issues in humans and wildlife.Given the options, oil and mercury are known to be significant pollutants that threaten water resources. However, since the question is a multiple-choice question and only one answer can be selected, and given the context of the question, oil is the most appropriate answer as it is a well-known and widespread threat to water resources.