For hours after their boat sank, Ken Henderson and Coen trod(踏) water in the Gulf of Mexico, talking about life and death while struggling to survive. For more than 30 hours, it worked.

    Then Henderson was forced to make a decision. “I'm going to go for help or you're not going to make it,” Henderson told Coen, just before cutting the strap(带子) that connected them in the deep, cold waters. “I understand,”Coen responded, giving Henderson a last set of instructions, “Kiss my babies for me.”

    Days after the fishing trip ended in tragedy, Henderson told the story for The Associated Press.

    They had been fishing for a few hours when suddenly Coen noticed the boat was filling with water. Henderson got both motors roaring, only to have the saltwater that had leaked in break them straight away…Coen jumped to the right, his sunglasses and cap flying off. The two grabbed extra life jackets and other floating items, including a half full bottle of Diet Coke.

    “The water was so cold and it took your breath away,” Henderson said. They immediately began to tremble.

    The pair prepared for a long wait. And they talked.

“We discussed things and discussed life. We discussed families. We just tried to keep occupied,” Henderson said.

    Eventually Coen started hallucinating(有幻觉). Henderson tried to keep Coen's arms and legs moving. But as morning came, Coen's situation worsened. And so Henderson decided to cut the strap.

    He swam for two hours, tired, frustrated and depressed. Then he saw an oil rig(钻探平台) in the distance. He swam, seeing ice and crystal trees in the water. He reminded himself constantly there were no trees.

    His legs was so weak that he could barely lift them. Henderson slowly pulled himself up the rig's ladder.

    It was over 50 miles from where they had gone in the water.

    All he could think of was Coen. Convinced his friend would survive, he told the coast guard where they had parted.

    Two hours later, a fisherman found a body in a life jacket.

    Later, in the hospital, Henderson saw his friend. He apologized and asked for forgiveness. He promised to realize his wishes and look after his girls.

    “I felt like a part of me had died out there,” Henderson said.

AaBb 1AB∶1Ab∶1aB∶1ab 配子间16种结合方式 子代中有9种基因型 4种表现型(9∶3∶3∶1)

如图所示，用一块轻塑料片挡住两端开口的玻璃筒下端，竖直插入水中并使塑料片距水面20cm，然后向玻璃筒内缓慢注入酒精(酒精密度为0.8x10³kg／m³)，当塑料片恰好下落时，注入酒精的高度为    (    )

图中AB为晨昏线的一部分，A为晨昏线上纬度最高点，C和D在同一纬线上，A、C、D三点所差经度数相同，此时地球公转速度较快。

黑藻是一种常见的沉水植物，其叶片小而薄，叶肉细胞内有大而清晰的叶绿体，液泡无色．某同学观察黑藻叶肉细胞的质壁分离和复原现象，实验步骤如图1．请回答下列问题：

（1）选用黑藻叶片观察质壁分离和复原实验现象的优点是____．

（2）步骤①中，要将视野右上方的叶肉细胞移到中央，应将装片向____移动．

（3）若步骤②中使用的试剂是0.3g/mL的蔗糖溶液，则在步骤③中观察到质壁分离现象，这是黑藻细胞发生____ 的结果．步骤④滴加清水后，步骤⑤观察到多数黑藻细胞不能发生质壁分离复原现象，最可能的原因是____．

（4）假设将黑藻三个相同的叶肉细胞分别放在a、b、c 3种不同浓度的蔗糖溶液中一段时间后，得到如图2所示状态（原生质层不再变化）．则结构②在3种溶液中的颜色差异____（明显/不明显），实验后结构③浓度的大小关系为____ ．

（5）近年来，人们发现黑藻也能利用有机碳进行混合营养生长，且光合速率得到提高．研究人员以醋酸盐补充有机碳源，研究其对黑藻光合色素含量的影响．实验结果如表：

不同醋酸钠浓度下黑藻中主要色素含量（mg/g）

①提取和分离黑藻叶中光合色素的操作如图3，图3中试剂A、B分别为____ ，操作C的要求是____ 

②由如表数据可推测，补充醋酸盐之所以能提高黑藻的光合速率，是因为____