Concept:Tides are periodic rises and falls of sea levels caused by gravitational attraction.Explanation:The Moon is the primary cause of tides, but it is not listed as an option.The Sun also exerts a strong gravitational pull on Earth's oceans.This solar gravity contributes to daily tides and greatly influences spring and neap tides.Since only the Sun is a realistic tidal influence among the choices, it is the correct option.Answer:D. the sun