$\overrightarrow{e_1}$、$\overrightarrow{e_2}$是不共线的向量，$\overrightarrow{a}$=$\overrightarrow{e_1}$+k$\overrightarrow{e_2}$，$\overrightarrow{b}$=k$\overrightarrow{e_1}$+$\overrightarrow{e_2}$，则$\overrightarrow{a}$与$\overrightarrow{b}$共线的充要条件是实数k等于（　　）

多吃紫菜等海产品可预防大脖子病，原因是它富含(   )

在做“测定金属丝的电阻率”的实验中，若待测金属丝的电阻约为5Ω，要求测量结果尽量准确，提供以下器材供选择：

A．电池组（3V，内阻1Ω）              

B．电流表（0～3A，内阻0.012 5Ω）

C．电流表（0～0.6A，内阻约0.125Ω）     

D．电压表（0～3V，内阻4kΩ）

E．电压表（0～15V，内阻15kΩ）         

F．滑动变阻器（0～20Ω，允许最大电流1A）

G．滑动变阻器（0～2 000Ω，允许最大电流0.3A）   

H．开关、导线若干

①实验时电流表、电压表、滑动变动阻选用____（填写仪器前字母代号）；

②测电阻时，电流表、电压表、待测金属丝电阻R_x在组成测量电路时，应采用电流表____接法，待测金属丝电阻的测量值比真实值偏____（选填“大”或“小”）；

③若用螺旋测微器测得金属丝的直径d的读数如图所示，则读数为____ mm；

④若用L表示金属丝的长度，d表示直径，测得电阻为R，请写出计算金属丝电阻率的表达式ρ=____．

    Industrial emissions (排放) of carbon dioxide and other planet-warming greenhouse gases have raised the global average temperature by about 0.8°C since the beginning of the Industrial Revolution. But studies have disagreed about what impact the rise is having on the world's species, says Mark Urban, an ecologist at the University of Connecticut, Storrs. Some have estimated that as many as 54% of species could eventually become extinct as a result of the climate change, but others have suggested no significant impact.①

    Such disparate result might originate from the limited nature of some individual studies, possibly because they focused only on a few species or a relatively small geographical region, says Urban.② To address these limits, Urban used statistical methods to help blend the results of previous studies into an apples-to-apples comparison that estimates the risk of extinction of species worldwide.

    ③He chose to analyze only the results of studies that had assessed extinction risks of more than one species. Then he researched into the details, such as the regions in which species considered, whether those species were limited to one small region or were widely spread, and whether the species were free to move as climate changed or were blocked by barriers such as mountain ranges or urban development.④

    Effects of climate change aren't always immediate, Urban says, and the risks of extinction he's estimated are the long-term results of species not being able to find a suitable habitat. Maybe the habitat will merely shrink to a size that can't support the species, or maybe it will disappear entirely. In some cases, he notes, a species might not be able to outpace the shift in its range, dying out before it can reach a new homeland. For over the generations that rapid warming might kill them off before they can spread to a suitable new habitat.