Topic 1 　For a decade, metallurgists studying the hulk of the Titanic have argued that the storied ocean liner went down quickly after hitting an iceberg because the ship's builder used substandard rivets that popped their heads and let tons of icy seawater rush in. More than 1,500 people died.

　　Now a team of scientists has moved into deeper waters, uncovering evidence in the builder's own archives of a deadly mix of great ambition and use of low-quality iron that doomed the ship, which sank 96 years ago Tuesday.

　　The scientists found that the ship's builder, Harland and Wolff, in Belfast, struggled for years to obtain adequate supplies of rivets and riveters to build the world's three biggest ships at once: the Titanic and two sisters, Olympic and Britannic.

　　Each required three million rivets, and shortages peaked during Titanic's construction.

　　"The board was in crisis mode," said Jennifer Hooper McCarty, a member of the team that studied the company's archive and other evidence. "It was constant stress. Every meeting it was, 'There's problems with the rivets, and we need to hire more people.' "

　　The team collected other clues from 48 Titanic rivets, using modern tests, computer simulations, comparisons to century-old metals and careful documentation of what engineers and shipbuilders of the era considered state of the art.

　　The scientists say the troubles began when the colossal plans forced Harland and Wolff to reach beyond its usual suppliers of rivet iron and include smaller forges, as disclosed in company and British government papers. Small forges tended to have less skill and experience.

　　Adding to the threat, the company, in buying iron for Titanic's rivets, ordered No. 3 bar, known as "best," not No. 4, known as "best-best," the scientists found. They also discovered that shipbuilders of the day typically used No. 4 iron for anchors, chains and rivets.

　　So the liner, whose name was meant to be synonymous with opulence, in at least one instance relied on cheap materials.

　　The scientists argue that better rivets would have probably kept the Titanic afloat long enough for rescuers to have arrived before the icy plunge, saving hundreds of lives.

　　Topic 1

　　1996年，一位摄影师在新疆喀纳斯自然保护区无意间拍到一只白熊。自此以后的十年里，白熊藏身于深山之中，再无音讯。直到2003年，人们才再次在该自然区又发现了白熊的踪迹。

　　在熊的家族里，只有北极熊是白色的。但是，这个庞然大物是如何离开极地寒带，来到这个寒温带的地方呢?难道它是通过通往北极的水路来到此地?这一猜测遭到动物学家的质疑。首先，北极熊不能在温带的树林中生活。其次，。。。。。。。。。

　　2006年，一个科学考察队在白熊出没的地区发现了熊冬眠的冬窝儿，还发现了一小团白色的动物毛发。DNA样本鉴定为棕熊的毛发。但是，也有可能，至少那团毛发不属于照片中的白熊。

　　Topic 2 　　蓝藻是一种简单的水生植物，它可以在河湖、湿地、树干和温泉自然蔓延生长。当蓝藻细胞达到一定程度时，蓝藻的“密集孽生”会使水体变色、引起泡沫、散发臭气、影响贝类和鱼类的生存，还会使水质大幅度下降。

　　2007年夏天，富营养物和其他污染导致蓝藻在太湖、巢湖、滇池发生了蓝藻“密集孽生”现象，影响了城市供水及水生产品生长。

　　“密集孽生”最严重的是太湖东部。太湖是我国第三大淡水湖。这次“密集孽生”导致周边100多万居民供水问题长达10天之久。为了防止污染，当地环保部门关闭了770家化工厂。

　　2008年夏天，长期的温暖、干燥气候导致蓝藻在部分地区发生。9月，一艘可以快速、有效地清除蓝藻的船在江苏省投入使用