超薄切片技术的步骤为（）。 A.取材、固定、脱水、包埋、切片、染色 B.取材、固定、

In order to protect valuable energy, snails(蜗牛) basically play a game of follow-the-leader, a new study finds. Snails create trails of mucus(黏液) to help them move smoothly across the ground, mainly in search of food or a partner, but making all that mucus uses up a lot of energy.

“Snails use a lot of energy, probably a third, creating mucus,” said Mark Davies of the University of Sunderland, lead author of the study published in the journal Proceedings of the Royal Society. “This process is very tiring indeed— much more so than walking, swimming or flying.”

Davies and his workmates studied marine snails off the coast of Britain and discovered that to save some of this important energy, the snails sometimes follow the existing mucus trails laid down by other snails to get around and so only have to create a small part of the mucus needed to make a new trail.

“The fact that they can make savings has an effect on as much as they have to save more energy to do other things like reproducing,” Davies said.

The energy saving may also help snails which live in environments where food is not enough, making the energy harder to replace.

Biologists had long guessed that snails behaved this way, but this is the first study to directly observe it. Davies said that it is likely that all snails use this means of cutting energy as they work hard through life.

45. What’s the function of mucus that snails create?

A. To find their food                   B. To find their way back

C. To save their energy                 D. To help them move smoothly

46. According to the passage, which of the following statements is TRUE?

A. The snail’s life is very hard.           

B. The snails don’t need much to reproduce.

C. This is the first time to do the guess.     

D. The snails will replace more energy in places lacking food.

47. From the passage we know that ______.

A. snails’ trails are sometimes reused     

B. snails’ food is difficult to find

C. snails can live a long life             

D. only marine snails have the ability

48. What does the passage mainly talk about?

A. How snails move and work.     

B. Snails save energy by reusing mucus trails.

C. A new study finds the mysteries of snails.

D. Snails make full use of their energy.

我国现行海洋经济管理体制的缺陷是什么？应如何改进？

引起重症手足口病的病毒是（）

A.埃可病毒

B.肠道病毒EV71型

C.柯萨奇CoxA16

D.腺病毒

E.EB病毒

我国新生代的地壳运动及其影响的岩浆活动的规模和程度是古生代以来任何时期都无法比拟的。

最基本的门电路有（）

A、与门

B、或门

C、非门

D、非与门