You can tell the age of a tree by counting its ring. But these records of a tree’s life really say a lot more. Scientists are using tree ring to learn what’s been 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 at elements in the rings from a certain years, scientists can tell what elements were in the air that year. Dr. Stevenson is analyzing one element, carbon-14, in ring from both living and dead tree. Some ring go back almost ten thousand year to the end of the Ice Age. When Stevenson followed the carbon-14 levels changed with the intensity of solar burning. You see, the sun has cycles. Sometimes it bums fiercely, and at other times it is relatively calm. During the sun’s violent periods, it throw off charged particles in fast moving streams called "solar winds". The particularly interfere with the formation of carbon-14 on earth. When there is more solar wind activity, less carbon-14 is produced. Ten thousand years of tree ring show that the carbon-14 level rises and falls about every 420 years. The scientists concluded that solar wind activity must follow the same cycle.
The underlined phrase "throw off" probably means ().
A. give away
B. cast
C. send for
D. get rid of
参考答案：D
解析：
根据“During the sun’s violent periods,…called ’solar winds’.”可知，在太阳活动剧烈期大量的粒子流会摆脱束缚而形成太阳风。give away意为“赠送，送出”；cast意为“投，掷，抛”；send for意为“派人去请”；get rid of意为“摆脱，除去”。