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问题 单项选择题

因各肿瘤发病的年龄分布不同，食管癌的峰型呈

A．单峰型

B．缓慢上升型

C．持续升高型

D．双峰型

E．侧峰型

答案

参考答案：C

解析：恶性肿瘤的年龄别发病率变动类型有4种。①婴儿期高峰型：发病率以婴幼儿时为多，以后明显下降，如肾母细胞瘤。②持续升高型：发病率随年龄持续升高，如胃癌、食管癌。③上升后下降型：发病率上升至一定年龄后下降，如肺癌的死亡率在75岁后有所下降。④双峰型：发病率在人生过程中可出现两个年龄高峰，如乳腺癌，一个高峰在青春期，另一个高峰在更年期。

单项选择题

用作行道树的苗木规格大体一致，相邻的同种苗木，高度相差不超过（）厘米。

A.50

B.60

C.70

D.80
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问答题

The produce departments of the future may look like nothing on earth, and with good reason. Chinese scientists have been growing tomatoes the size of softballs, cucumbers as long as baseball bats and other outsize fruits and vegetables, using seeds that have been shot into space. The seeds are then exposed to seven types of extraterrestrial conditions, from zero gravity and cosmic radiation to subatomic particles. (46) As these space veggies grow back on earth, they are selected for desirable traits--bulk, appearance or certain nutrients--then bred through successive generations to ensure that the mutations are consistent.
Chinese scientists don’t understand exactly how a trip into space alters the seeds’ DNA and yields such effects, but it’s not just size that changes. (47) Tong Yichao, whose firm, the Beijing Flying Eagle Green Foods Group, has been sending seeds and seedlings aboard Chinese spacecraft since 1999, says it has grown space tomatoes with 27 percent more of the antioxidant beta carotene than ordinary ones, and six-foot-tall cotton plants that produce longer, more flexible threads. Using conventional methods, "a scientist might create just three new plants in his lifetime," says Tong. "We’ve developed more than 50 since 1999."
(48) A dozen or so Chinese firms are paying up to $ 45 000 a gram to place various flora aboard satellites and manned spacecraft. The long-term goal: to feed more people and help endangered species escape extinction. To date, nearly 3 000 botanical species-including garden vegetables, medicinal herbs and flowers--have been sent into orbit and brought back to earth.
(49) The commercial promise of China’s space veggies has yet to, er, bear fruit. It’ s legal to sell the cosmic produce, and commercial farms have purchased some space plants. But most are being developed in labs or experimental greenhouses because no one wants to go to market before the safety and quality of the produce have been established. Even so, the idea of space flora is proving irresistible to a novelty-loving Chinese public. (50) When Tong displayed a handful of monster space eggplants--the largest of which weighed more than four pounds--at an expo, one disappeared before the show opened. Hot stuff, for sure.
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