| Humans on the earth have had an over-inflated view
of how far the planet’s atmosphere extends into space. It turns out that the
ionosphere (电离层), the layer of electrically charged particles that comprises the
outer atmosphere, is thinner than expected-and cooler. Understanding the shape and size of the ionosphere is an important first step in figuring out how particularly dense regions within it may distort radio, radar and navigation signals. Such distortions can make communications and satellite-based systems less reliable. "In order to predict how severe those distortions will be, it’s necessary to know how big those structures in the ionosphere are and where they exist," Roderick Hellis, with the Space sciences Center at the University of Texas in Dallas, told Discovery News. Hellis and his colleagues have been using a suite o A. how far away the upper edge of the ionosphere is B. how many particles comprise the ionosphere C. how long the ionosphere has been existing D. how the ionosphere extends into space [单项选择]
Like all other mothers who have small children, I, too, have to steal time--from my own children at home and from the children who know me as their teacher--just to put a few words down on paper. Many times I’ve wanted to write for myself, for other women, for my parents, for my husband, and especially for my children. I would have liked to leave a legacy (遗产) of words explaining what it has meant to have twins (双胞胎). One reason there is not a great deal written about being a mother of a new baby is that there is seldom a moment to think of anything else but the baby’s needs. 我来回答: 提交
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