The plant "sumpweed" is mentioned in line 25 in order to（） A: contrast a plant with high nutritional value with one with little nutritional value B: explain the medicinal use of a plant C: clarify which plants grew better in places where trees were not cut down D: provide an example of a plant that was easy to domesticate

1. How did human being become effective hunters? A: Human body is especially adapted to be good hunters. B: Human beings were biological superior that helped us to become effective hunters. C: Human beings were born with a bigger brain and became effective hunters. D: Human beings were able to domesticate animals to become effective hunters. E: Human beings were physically weak and we had to develop tools to become effective hunters.