When Columbus reached the New World, com was the most widely grown plant in the Americas. This plant’s range extended from what is now southern Canada to lower South America. At that time some tribes cultivated it at sea level, others at elevation(海拔高度) of more than 11 000 feet.
"Columbus had no way of knowing that corn was far more valuable than the spices(香料) and gold he had hoped to find." said Frances B. King, a professor at a university of Pittsburgh. Through human intervention, this plant has developed into several hundred races, or varieties. Their heights vary from 2 to 12 feet, and their maturity ranges from little more than 2 months to almost a year. Their ears vary not only in color, but also in size.
Unlike other cereals(谷类), corn bears little resemblance to its wild ancestors. In fact, it differs from the appearance of its immediate ancestors more than any other cultivated plant known. From humble origins as a lowland grass, corn devel
A. a new revolution
B. new findings about corn
C. the signs of com 5 500 years ago
D. new dates for communities’ emergence
When Columbus reached the New World, com was the most widely grown plant in the Americas. This plant’s range extended from what is now southern Canada to lower South America. At that time some tribes cultivated it at sea level, others at elevation(海拔高度) of more than 11 000 feet.
"Columbus had no way of knowing that corn was far more valuable than the spices(香料) and gold he had hoped to find." said Frances B. King, a professor at a university of Pittsburgh. Through human intervention, this plant has developed into several hundred races, or varieties. Their heights vary from 2 to 12 feet, and their maturity ranges from little more than 2 months to almost a year. Their ears vary not only in color, but also in size.
Unlike other cereals(谷类), corn bears little resemblance to its wild ancestors. In fact, it differs from the appearance of its immediate ancestors more than any other cultivated plant known. From humble origins as a lowland grass, corn devel
A. was mainly grown at sea level
B. was not grown below the elevation of 11 000 feet
C. was widely grown in Canada only
D. spread throughout Americas
New York: when the first jet struck World Trade Center at 8:48 a.m. on Tuesday, the people in 2 World Trade Center with a view of the instant damage across the divide had the clearest sense of what they, too, must do: get out fast.
Katherine Hachinski, who had been knocked off her chair by the blast of heat exploding from the neighboring tower, was one of those. Despite her 70 years of age, Ms Hachinski, an architect working on the 91st floor of 2 World Trade Center, the south tower, went for the stairs. Twelve floors above her, Judy Wein, an executive (经理), screamed and set off too.
But others up and down the 110 floors, many without clear views of the damage across the way and thus unclear about what was happening, were not so sure. And the 18 minutes before the next plane would hit were ticking off.
Amid the uncertainty about what was the best thing to do, formal announcements inside the sound tower instructed people to stay put, assuring them t
A. keep silent
B. leave at once
C. put everything back and then leave
D. stay in the building
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