Questions 14 to 17 are based on the passage you have just heard.
14. What does the nest built by tailor bird look like?
15. Why is there a hole in the weaver birds nest?
16. What is the oven birds nest made of?
17. What might surprise us about birds nests according to the speaker?
Passage Three
You can tell the age of a tree by counting its rings but these records of trees life really say a lot more. Scientists are using tree rings to learn whats being happening on the suns surface for the last ten thousand years. Each ring represents a year of growth. As the tree grows it adds a layer to its trunk taking up chemical elements from the air. By looking up the elements in the rings for a given year scientists can tell what elements were in the air that year. Doctors Stevenson is analysing one elementcarbon-14 in ring from both living and dead trees. Some of the rings go back almost ten thousand years to the end of the Ice Age. When Stevenson followed the carbon-14 trail back in time he found carbon-4 levels change with the intensity of solar burning. You see the sun has cycles. Sometimes it burns fiercely and other times its relatively calm. During the suns violent periods it throws off charged particles in fast moving strings called solar winds. The particles interfere with the formation of carbon-14 on earth. When theres more solar wind activity less carbon-14 is produced. Ten thousand years of tree rings show that the carbon-14 level rises and falls about every 420 years. The scientists concluded that the solar wind activity must follow the same cycle.
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