为预防小儿的上呼吸道感染对家长的错误建议是（） A．实行母乳喂养 B．预防营养不良

Many people consider the wider use of biofuels a promising way of reducing the amount of surplus carbon dioxide (CO₂) being pumped into the air by the world’s mechanized transport. The theory is that plants such as sugar cane, maize (corn, to Americans), oilseed rape and wheat take up CO₂ during their growth, so burning fuels made from them should have no net effect on the amount of that gas in the atmosphere.

Theory, though, does not always translate into practice, and just as governments have committed themselves to the greater use of biofuels, questions are being raised about how green this form of energy really is. The latest comes from the International Council for Science (ICSU) based in Paris.

The ICSU report concludes that, so far, the production of biofuels has aggravated rather than ameliorated global warming. In particular, it supports some controversial findings published in 2007 by Paul Crutzen of the Max Planck Institute for Chemistry in Germany. Dr. Crutzen concluded that most analyses had underestimated the importance to global warming of a gas called nitrous oxide (N₂O). The amount of this gas released by farming biofuel crops such as maize and rape probably negates by itself any advantage offered by reduced emissions of CO₂.

Although N₂O is not common in the Earth’s atmosphere, it is a more potent greenhouse gas than CO₂ and it hangs around longer. The result is that, over the course of a century, its ability to warm the planet is almost 300 times that of an equivalent mass of CO₂.

N₂O is made by bacteria that live in soil and water and, these days, their raw material is often the nitrogen-rich fertiliser that modern farming requires. Since the 1960s the amount of fertiliser used by farmers has increased sixfold, and not all of that extra nitrogen ends up in their crops. Maize, in particular, is described by experts in the field as a “nitrogen-leaky” plant because it has shallow roots and takes up nitrogen for only a few months of the year. This would make maize (which is one of the main sources of biofuel) a particularly bad contributor to global N₂O emissions.

But it is not just biofuels that are to blame. The ICSU report suggests N₂O emissions in general are probably more important than had been realised. Previous studies, including those by the International Panel on Climate Change (IPCC), a United Nations-appointed body of experts, may have miscalculated their significance — and according to Adrian Williams of Cranfield University, in Britain, even the IPCC’s approach suggests that the global-warming potential of most of Britain’s annual crops is dominated by N₂O emissions.

Scientists realize that maize（）

A. contributes little to global N₂O emissions

B. absorbs nitrogen very efficiently in crops

C. is largely responsible for the surplus N₂O

D. may experience a bad harvest for bacteria

—You look worried. _______?

—My new car hit a tree yesterday. [ ]

A. What's up

B. What do you beckon

C. Can I do a favour

D. How do you do

As we know, no matter how        a man is, if he doesn’t learn, he knows nothing.

A．intelligent

B．enthusiastic

C．relaxed

D．disappointed

为了探究二氧化碳能否与水发生反应生成具有酸性的物质，A、B两同学分别设计了探究实验的方案。A同学的实验方案是将二氧化碳通入紫色石蕊试液中，观察溶液的颜色变化，如图甲所示。B同学的实验方案是取四朵用石蕊试液染成紫色的干燥的小花，按图乙进行实验，观察小花颜色变化(紫色石蕊试液遇酸变红色)。

(1)图乙中，观察到纸花的颜色变化是：I．纸花变红 Ⅱ．      Ⅲ．纸花不变色 Ⅳ．       

写出实验Ⅳ中发生反应的文字表达式：                            。

（2）哪个同学的方案合理          。

(3)该方案合理的理由是                             。

某型手动静态平衡阀的全开阻力均为30kPa，在所示的空调水系统图中（未加平衡阀），各支路的计算水阻力分别为：PAB=90kPa、PCD=50kPa、PEF=40kPa，如果主干管的水阻力忽略不计，问：设置静态平衡阀时，合理的设置方法应是下列选项的哪一个？（）

A.在1、2、3、4点均应设置静态平衡阀

B.只在2、3、4点设置静态平衡阀

C.只在2、3点设置静态平衡阀

D.只在2点设置静态平衡阀