In the 1960s and ’70s, teams of engineers and computer scientists worked to build the foundation for a network of networks. （Para. 1）（）

Plenty of sand is the natural condition for the being of polders. From the letter we can learn that Sand River _______. In the 1960s and ’70s, teams of engineers and computer scientists worked to build the foundation for a network of networks. （Para. 1）（） A truck loaded with sand accelerates along a highway. The driving force on the truck remains constant. What happens to the acceleration of the truck as its trailer leaks sand at a constant rate throug The traditional Navaho does not allow copying of sand paintings because ______. The fact that reproductions of sand paintings are now commercially available shows that ______. What does a sand dollar look like according to Kara? The cast iron was melted and _____ into sand molds as soon as possible. For（）commodities as oil, sand and timber, rail is cheaper than road. As far as the European market is concerned, the writer thinks that Sand River products _______. When I passed the river, I saw some children ______ on the sand. As far as the European market is concerned, the writer thinks that Sand River products______ . The artist is so （） that he can make different changing pictures with sand. Their teacher was ill, so they sat inthe classroom__________.[ ] In summer Mary likes to walk along the beach with _________feet, leaving footprints on the sand.[ ] When ________ on sand, the plant grows close to the ground, ________ narrow leaves and small flowers. [ ] It’ll stop the sand from moving_____the rich farm land in the south.[ ] People have planted a great many trees in order to __________ wind and sand in the desert. [ ] People have planted a lot of trees and grass in order to ____ wind and sand in the desert. ___the clouds, you would find the airplane inthe sky easily