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，一位攝影師在新疆喀納斯自然保護(hù)區(qū)無意間拍到一只白熊。自此以后的十年里，白熊藏身于深山之中，再無音訊。直到2003年，人們才再次在該自然區(qū)又發(fā)現(xiàn)了白熊的蹤跡。

　　在熊的家族里，只有北極熊是白色的。但是，這個(gè)龐然大物是如何離開極地寒帶，來到這個(gè)寒溫帶的地方呢?難道它是通過通往北極的水路來到此地?這一猜測遭到動(dòng)物學(xué)家的質(zhì)疑。首先，北極熊不能在溫帶的樹林中生活。其次，。。。。。。。。。

　　2006年，一個(gè)科學(xué)考察隊(duì)在白熊出沒的地區(qū)發(fā)現(xiàn)了熊冬眠的冬窩兒，還發(fā)現(xiàn)了一小團(tuán)白色的動(dòng)物毛發(fā)。DNA樣本鑒定為棕熊的毛發(fā)。但是，也有可能，至少那團(tuán)毛發(fā)不屬于照片中的白熊。

　　Topic 2 　　藍(lán)藻是一種簡單的水生植物，它可以在河湖、濕地、樹干和溫泉自然蔓延生長。當(dāng)藍(lán)藻細(xì)胞達(dá)到一定程度時(shí)，藍(lán)藻的“密集孽生”會(huì)使水體變色、引起泡沫、散發(fā)臭氣、影響貝類和魚類的生存，還會(huì)使水質(zhì)大幅度下降。

　　2007年夏天，富營養(yǎng)物和其他污染導(dǎo)致藍(lán)藻在太湖、巢湖、滇池發(fā)生了藍(lán)藻“密集孽生”現(xiàn)象，影響了城市供水及水生產(chǎn)品生長。

　　“密集孽生”最嚴(yán)重的是太湖東部。太湖是我國第三大淡水湖。這次“密集孽生”導(dǎo)致周邊100多萬居民供水問題長達(dá)10天之久。為了防止污染，當(dāng)?shù)丨h(huán)保部門關(guān)閉了770家化工廠。

　　2008年夏天，長期的溫暖、干燥氣候?qū)е滤{(lán)藻在部分地區(qū)發(fā)生。9月，一艘可以快速、有效地清除藍(lán)藻的船在江蘇省投入使用