A、To illustrate the size of some objects. B、To introduce the next assignment. C、To show some artifact on display at the campus m

Today’s lecture we’ll center on the prehistoric people of Nevada Desert. Now most of these prehistoric desert people moved across the countryside throughout the year.(16)You might think that they’re wandering aimlessly. Far from it, they actually followed the series of carefully planned moves. Where they moved depended on where food was available. Places where plants were ripe-ning or fish were spawning. Now often when these people moved, they carried all their possessions on their backs. But if the journey was long, extra food and tools were sometimes stored in caves 01 beneath rocks. One of these caves is now an exciting archaeological site. Beyond its small opening is a huge underground grotto.(17)Even though the cave is very large, it was certainly too dark and dusty for the travelers to live in. But it was a great place to hide things.(18)And tremendous amounts of food supplies and artifacts have been found there. The food includes dried fish, seeds and nuts. The artifacts include stone spear points and knives. The spear points are actually rather small.(19)Here is a picture of some that were found. You can see their size in relation to the hands holding them.
16. What point does the speaker make about the prehistoric people of the Nevada Dessert?
17. Why didn’t the people live in the cave described by the speaker?
18. What have archaeologists found in the cave?
19. Why does the speaker show a photo to the class?