A) Wetlands act as natural filters, absorbing and transforming excess nutrients like nitrogen and phosphorus, thus preventing eutrophication in downstream waters. B) While the wording "releasing heavy metals" is imprecise, wetlands are known to remove heavy metals from water through processes like absorption by plants (phytoremediation), adsorption to sediments, and microbial activity. This removal from the water column is a beneficial function, managing and retaining heavy metals within the ecosystem rather than releasing them into the wider environment. C) Wetlands slow down water flow, allowing suspended sediments to settle out. This reduces siltation in rivers and other water bodies.