The right option is; d. things discarded by humans
Marine debris is best described as things discarded by humans.
Marine debris is any human made, solid substances that has be intentionally or unintentionally released in a lake, stream, sea, ocean, or waterway. Marine debris may be composed of simple items such as a plastic bag, bottles, glass or cans that enter the water body potentially injuring and killing marine life. Almost all marine debris comes from land-based sources.