听力原文： 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 tings to learn what's being happening on the sun's 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 analyzing one element—carbon-14 in ring from both living and dead trees. Some of the tings go back almost ten thousand years to the end of the Ice Age. When Stevenson followed the carben-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 it's relatively calm. During the sun's violent periods, it throws off charged particles in fast moving strings called solar winds. The particles interfere with the formation of carben-14 on earth. When there's 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.

What can the tree's rings tell us？

A．The age of the tree.

B．The changing activities of sun.

C．A lot more.

D．All the above.