The Great Wall is more than 13, 000 miles in total. As a symbol     1     China, it is the longest wall in the world. It was     2     (finish) in parts through 2,000 years. In ancient world, people     3     (usual) pressed natural materials such as soil and rocks together to build walls. It was called “rammed earth”. In some areas, the Great Wall was built using rammed earth. Over time, wind and rain can easily break down rammed earth,     4     scientists often wondered how these old parts of the Great Wall have remained for such a long time. A group of Chinese researchers examined a 370-mile long part of the wall. They found that more than 2/3 of it was covered by something called biocrusts (生物结皮). They are thin layers (层) of different     5     (kind) of plant lives. The scientists     6     (take) some of the biocrusts back for testing. The result showed that they were     7     (strong) than rammed earth. It means biocrusts play a key role in     8     (protect) the Great Wall from erosion (侵蚀). These findings could be important for people who study ancient structures around     9     world. Although biocrusts may not look good,     10     (they) ability could be a very useful tool to keep ancient buildings.

Beachcombing is a popular activity these days. What is that? It means going to the beach and looking for interesting objects by the sea. Are you interested in it?     1    

Be prepared

Ask an adult to check the tides (潮汐) before you go.     2     It is best to go beachcombing 2 or 3 hours before or after low tide. So you can see the beach clearly. Dress in warm and comfortable clothes and wear wellies (雨靴). Prepare a bag for collecting objects.

Get searching

Don’t rush on the beach.     3    You should try to find some holes in the wet sand. Some creatures like starfish and crabs (螃蟹) will be seen there.

Record and learn

    4     Then you can check them out when you are back home to find out more about them. It’s also a way for you to learn something new. Knowledge is not only kept in books, but also in life.

Improve the environment

Many objects on the beaches are part of the nature. If you see something interesting, leave it there.     5     For example, pick up plastic bags and bottles.