敌人使用化学武器的迹象

It is easy for us to tell who our family members are, but do plants recognize(识别) their own family? Some do, scientists say, according to a report by Science News in early 2010.

Guillermo P. Murphy and Susan Dudley are two plant scientists from McMaster University in Hamilton, Canada. They did a few experiments with Jewelweeds, a kind of flower that grows in wet, shady spots. They found that the flowers seem to know their own flower family. In their experiments, Murphy and Dudley planted jewelweeds in pots with either siblings or strangers.

When jewelweeds were planted in pots with strangers, the plants started to grow more leaves than if they had been planted alone. This response(反应)suggests that plants are competing with strangers for sunlight, since a plant with more leaves can receive more light and make more food. Jewelweeds usually grow in the shade, where sunlight is not enough.

When jewelweed seedlings(幼苗)were planted with siblings, they grew a few more branches than they usually would if they were alone – but they did not start growing lots of extra leaves. This behavior suggests the plants are more likely to share resources, rather than compete.

According to the Science News report, Jewelweeds are not the first plants that plant scientists have studied for family recognition. In 2007, Dudley and her team studied the Great Lakes sea rocket, a plant that grows on the beach – where it may be hard to get fresh water. In that experiment, the scientists found that when sea rockets were planted with siblings, they tolerated each other. But when they were planted with strangers, the sea rockets reacted by working extra hard to grow lots of roots.

Dudley says this just because sea rockets, on the beach, get plenty of sun but struggle for water – so when they’re threatened, they compete for water. Jewelweeds have plenty of water but have to compete for sunshine, so they grow more leaves.

小题1: What does the underlined word siblings mean?

A．Flowers come from foreign countries.

B．Plants growing in different environments.

C．Flowers planted with lots of strangers.

D．Plants that are the same kind.小题2: In the text, the writer mentioned the experiments of Jewelweeds to         .

A．make a comparison

B．introduce a topic

C．describe a pretty flower

D．build a new theory小题3: According to the passage, flowers planted alone will         .

A．grow more leaves than those planted in groups

B．become taller than those with more branches

C．grow fewer leaves than those planted with strangers

D．become ill easily because they can’t get enough shade小题4: What can be the best title for the passage?

A．New Discoveries about Plants

B．How Plants Compete with Each Other

C．Family Recognition among Plants

D．Jewelweeds and the Great Lakes Sea Rockets

晚上，小亮走在大街上．他发现：当他站在大街两边的两盏路灯之间，并且自己被两边路灯照在地上的两个影子成一直线时，自己右边的影子长为3米，左边的影子长为1.5米．又知自己身高1.80米，两盏路灯的高相同，两盏路灯之间的距离为12米．则路灯的高为______米．

某奶牛场的奶牛于2008年8月上旬发生一次迅速流行的发热性疾病。病牛高热，体温高达41℃左右，精神委顿，食欲废绝，鼻镜干燥，呼吸加快，(每分钟达80次以上)，大量流涎，口角出现多量泡沫状黏液，头颈伸直，张口仲舌，呼吸极度困难，喘气声粗粝如拉风箱，肺泡音及支气管音增强；眼结膜充血浮肿，流泪，流鼻液呈黏性线状；喜卧懒动，严重者卧地不起；孕牛发生流产，有的产出死胎。大多数病牛的病情经3d左右逐渐减轻，很少发生死亡。

如需作进一步确诊，不能采用的方法是

A．血液涂片镜检 B．中和试验 C．琼脂扩散试验 D．免疫荧光抗体技术
E．补体结合试验及ELISA

桥式起重机接地体的制作时，可选用专用接地体用50mm×50mm×5mm（），截取长度为2.5m其一端加工成尖状。

A、铁管

B、钢管

C、角铁

D、角钢

三相交流电路中，流过每相电源或每相负载的电流叫做（）。

A、相电压

B、相电流

C、线电压

D、线电流