Answer:
a). acid rain.
Step-by-step explanation:
Sulfur dioxide is an invisible gas with sharp smell. Excessive sulfur dioxide in air can cause acid rain. When sulfur dioxide combines with air and water, sulfuric acid is formed, which is a major component of acid rain.
Acid rain causes deforestation and harm to aquatic animals when it gets mixed with ocean and river.
Thus, the correct answer is option (a).