题目

 I was born poor. Often we hadn’t enough to eat. Whenever we had some food, Mother often gave me her portion of rice. While she was   21   her rice into my bowl, she would say, “ Eat this rice, son! I’m not hungry.”     As I grew, Mother    22   her spare time to fish in a river; she hoped that she could give me a bit more nutritious food for my   23   . Once she caught just two fish, and she made fish soup. While I was eating the soup, Mother would sit beside me and eat   24   was still left on the   25   of the fish I had eaten. My heart was   26 在海洋生态系统中，氧气在水中的分布含量是不同的，具体见图曲线所示，请对曲线仔细分析后回答下列问题： （1）表层海水中含氧量最高的原因是____________________________________。 （2）表层以下海水中的溶解氧的变化主要是______________________________。 （3）实际结果表明，在正常条件下，缺氧层在100 m～150m水层，请分析其原因：________________________________________，向下则又稍为增加，其原因是________________________________________。 （4）在海洋生态系统中，限制海洋生物分布的主要因素除了图中所示的外，还有________等。 （5）由于“赤潮”的影响，一条4kg重的杂食性海洋鱼死亡，假如此杂食鱼的食物有1/2来自植物、1/4来自草食鱼类、1/4来自以草食鱼类为食的小型肉食性鱼类，按能量流动效率20％计算，该杂食性鱼从出生到死亡，共需海洋植物________kg。