Answer:
Sediment in rivers gets deposited as the river slows down. Larger, heavier particles like pebbles and sand are deposited first, whilst the lighter silt and clay only settle if the water is almost still.
Carbon dioxide because people in other animals exhale carbon dioxide as a waste product. People and other animals need oxygen for plants produce oxygen during an important process called photosynthesis which turns the sun energy into nutrients so carbon dioxide would be the answer.
