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Part One Initial consonants and consonant clusters English words begin with no, one, two, or three consonants. A. Listen and repeat. Read across the chart. The first word has no initial consonant. No
4+1听力口语MP3
Part One Initial consonants and consonant clusters English words begin with no, one, two, or three consonants. A. Listen and repeat. Read across the chart. The first word has no initial consonant. No
4+1听力口语MP3
We are traveling upwards away from our solar system, out of the spiral arms of the Milky Way. In front of us, lie vast clusters of stars, satellite groups that orbit the heart of our galaxy. These are globular clusters, over 150 have been discovered.
自然百科2011年
Measuring the brightnesses and colors of the stars in the globular cluster, we can figure out how old they are. Here is the remarkable thing: they are very old. Globular clusters, at least the stars in the globular clusters, in many cases, are almost
自然百科2011年
One of the puzzles about our galaxy is that we know that it's had stars forming continuously for about the last ten billion years. But at the rate/ it's eating up its gas now, it's forming new stars, it should burn out that gas soon, should run out o
自然百科2011年
But if you look carefully, stars aren't spread smoothly across the whole sky. They are gathered together into a band that loops around the sky which we call the Milky Way. That bright strip across the sky with its extraordinary abundance of stars and
探索与发现2013年