问题 选择题

能量在食物链的传递中递减,而农药残留在食物链中却(  )

A.少量增加

B.富集

C.减少

D.不变

答案

动物直接或间接地以植物为食,从而使物质和能量沿着食物链和食物网在生态系统的各营养级中流动.有毒物质会通过食物链不断积累,营养级别越高的生物,体内积累的有毒物质就越多,因为环境中有些污染物(如重金属、化学农药等)具有化学性质稳定、不易分解的特点,会在生物体内积累而不易排出;随着营养级的升高而不断积累,最终危害到人类的安全(富集).

故选:B

单项选择题
单项选择题

Home prices slid in November, raising questions about whether the housing recovery is robust enough to maintain a sustained turnaround. From October to November, home prices fell 0.2% after (1) 0.1% in October, according to a report Tuesday by Standard & Poor’s/Case-Shiller’s home price index. (2) five of the 20 metro areas (3) by the index saw price increases for the month.

On a(n) (4) basis, prices were 5.3% lower in November than in November 2008. Prices were the same as in late 2003. "What we’ve seen (5) the past couple of months is that the pace of (6) has fallen down," says Maureen Maitland of Standard & Poor’s. "Some markets have (7) Is that because we haven’t (8) the foreclosure (回赎权的取消) cycle Because of unemployment We’re not seeing the (9) we were seeing in the last summer months. "

Metro areas that have seen a retreat in home prices (10) Seattle, Charlotte, Las Vegas and Tampa. All four (11) gains they made in recent months (12) . (13) , for the 20-metro index, the annual rate of decline is improving. That (14) , with other recent housing reports that show prices (15) or accelerating, could point to (16) the housing market is starting to (17) its footing, some economists say. Existing home sale prices were $178 300 in December, which is 1.5% higher than December 2008, according to a report this week by the National Association of Realtors. That was the first year-over-year (18) in median price since August 2007.

"The most (19) thing we can say is not only the market is stabilizing, but we’ve seen that housing demand is p," says Bernard Baumohl, with the Economic Outlook Group. "Housing probably will continue to climb upwards through the summer, (20) it could slip a little as the tax credit expires. \

18()

A.gain

B.accomplishment

C.achievement

D.success