[填空题]Columbus reached America earlier than Magellan.

[填空题]Columbus reached America earlier than Magellan.

[填空题]In ______, Columbus reached North America.

[单项选择]

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

[单项选择]Not until Columbus discovered America ______ to Europe.
A. bananas were brought
B. are bananas brought
C. bananas brought
D. were bananas brought

[填空题]Wilhelm Stantien died earlier than Moritz Becker.

[填空题]Shakespeare began his poems no earlier than 1594.

[单项选择]Getting up earlier than usual or sleeping a couple of hours late can have a significant effect on your mood, according to research published in 1997. When the body’s internal clock, or circadian (生理节奏的) rhythm, gets (67) of accord with your sleep-wake (68) , you can be left (69) out of sorts.
Researchers have long known that moods vary along (70) fluctuations in functions regulated by the body’s (71) 24-hour cycle rhythm, such as body temperature and hormone levels. The (72) of time a person has been awake is also known to (73) mood. To tease apart the two effects, U.S. and U.K. researchers (74) 24 healthy volunteers to live in (75) chambers for approximately three to five weeks and (76) their sleep-wake cycles to (77) a 30-hour or a 28-hour day, (78) than the 24-hour schedule (79) by the rotation of the Earth. Circadian rhythms, which are innate, remained (80) <