Which of the following best describes the differnce between a source and a mouth? a) a source is where a river or stream originates, and a mouth is where it empites into another body of water? . b) a source is where a river or stream empties into another body of water, and a mouth is where it originates.? c) a source is partially surrounded by land, and a mouth is completely surrounded by land.? d) a source is completely surrounded by land, and a mouth is partially surrounded by land.