Final answer:
Paragraph 3 provides context for the reader on the significance of the atmosphere in the water cycle, along with detailing the underlying physical processes involved.
Step-by-step explanation:
Paragraph 3 was included at the beginning of the passage to inform the reader that the atmosphere plays a role in water cycles. This paragraph sets the stage for a deeper understanding of the complex processes involved in the water cycle, emphasizing that water cycles through different states and distinct reservoirs like oceans, glaciers, and the atmosphere, driven by solar energy and gravity. It is an essential context that highlights both the cyclical nature of the water cycle and the variety of physical processes by which water changes its state and moves through the Earth's system. Therefore, the correct answer is D. to inform the reader that the atmosphere plays a role in water cycles.