What evidence would a scientist need to find in order to show that Vikings used Icelandic spar for ship navigation?

Which of the following warnings would an agricultural chemist tell a farmer who wants to recycle his or her own ammonia? recycling ammonia is a difficult process that sometimes takes weeks. recycling ammonia requires a degree in biochemistry or a related field. recycling ammonia can be harmful because it is highly flammable and toxic. recycling ammonia costs too much money considering the price of the necessary chemicals.