若任一n维非零列向量都是n阶矩阵A的特征向量，证明A是数量矩阵(即A=kE，E是n阶

Thousands of puffins(海鹦) live in Maine and on islands in the Gulf of Maine. But the puffins may be in danger. Last summer, the percentage of laid eggs that successfully produced baby puffins took a dive. Scientists also found a decline in the average body weight of the adult and baby puffins on Machias Seal Island, home to the area’s largest colony. Over the winter, dozens of the seabirds from the region were found dead, likely from starvation.

What’s causing the puffin trouble? Scientists think it may be a shortage of food. With ocean temperatures rising, fish populations have moved around. Normally, puffins’ primary food source is herring, a type of fish. A lack of herring in the area could be causing the problem.

Butterfish from the south have become more abundant in the Gulf of Maine and could be a new food source for birds. But Steve Kress says butterfish may be too big and round for baby puffins to swallow.

Puffins spend most of their lives at sea. They come ashore to breed each spring and return to the ocean in August. The chicks swim to sea about 40 days after hatching. Puffin populations stretch across the North Atlantic, from Maine to northern Russia.

Maine’s puffin population has been at risk in the past. In the 1800s, they were hunted for their food, eggs and feathers. By 1901, only one pair of puffins remained in the state. Thanks to the help of local lighthouse keepers and seabird restoration programs, the state’s puffin population has been restored to more than 2,000 birds.

Scientists aren’t sure what will happen to the Gulf of Maine’s puffins. The birds may move further north. Kress says he hopes the Gulf population will sustain itself and then he continued. “You never know what climate change will bring,” Kress said. “Historically fish could move out and more southerly fish could move in, and puffins may adapt to the new fish. Only they will know how the story will unfold.”

小题1:The underlined phrase “took a dive” means _______.

A．increased

B．arose

C．reduced

D．changed小题2:In the scientists’ opinion, ________ is contributing to the puffin trouble.

A．a lack of herring

B．environmental pollution

C．the increase of birds

D．the huge size of butterfish小题3:It can be inferred from the passage that _______.

A．Maine’s puffin once nearly became extinct

B．Maine’s puffins’ eggs were of high prices

C．baby puffins grew up quickly

D．the number of Maine’s puffins is worrying小题4:Judging from Kress’s words in the last paragraph, we know ________.

A．climate change matters little

B．there is cause for concern

C．the new fish won’t harm puffins

D．puffins may move to the south小题5:How is the second paragraph mainly developed?

A．By giving examples.

B．By making comparisons.

C．By following time order.

D．By asking questions

直流-感应电诊断结果中绝对变性反应为（）

A.肌肉和神经对直流电刺激均无反应

B.神经对直流电刺激无反应，但是肌肉反应存在

C.神经对直流电刺激无反应或兴奋阈值增高；但对直流电刺激有反应

D.神经肌肉对感应电和直流电刺激的反应正常而兴奋阈增高

E.临床表现为瘫痪

根据《建筑工程资料管理规程》的有关规定，一个项目进行公开或邀请施工单位招投标，其过程中须形成的文件资料包括（）。

A.施工招投标文件

B.施工图

C.施工合同

D.结算书

E.概算书

一产妇为恢复体形，最佳体操锻炼时间为

A．产后42周

B．产后12周

C．产后1个月

D．产后24周

E．产后1周

化工企业常用的灭火剂有哪些？