已知M= $\frac{2}{9}$ a﹣1，N=a²﹣ $\frac{7}{9}$ a（a为任意实数），则M、N的大小关系为（　　）

（I）求数列{a_n}的通项公式；

（Ⅱ）令b_n=（2n﹣1）a_n，求数列{b_n}的前n项和T_n．

请根据所学知识，简述下列现象的原因．

（1）明明生病了，几天吃不下食物，身体明显消瘦了．这是因为贮存在体内的____ 等营养物质消耗多而补充少的原因．

（2）医生检查后，建议明明点滴葡萄糖液来恢复体力．这是因为葡萄糖能为身体提供____ ，葡萄糖、淀粉、蔗糖都属于____ 

（3）明明康复以后，妈妈每天都让他多吃奶、蛋、鱼、肉，是因为这些食物中含有丰富的____ ．人的生长发育以及受损细胞的修复和更新，都离不开它．

（4）小明有一段时间，每到傍晚的时候就看不清东西，妈妈让他坚持每天吃点熟胡萝卜，这种现象就消失了．原因是于____ 

（5）广告中说“补钙关键在吸收”，除了补钙外，还应补充____ ．

如图所示的木块浸没在水中，细线对木块的拉力是2N。剪断细线，待木块静止后，将木块露出水面的部分切去，再在剩余的木块上加1N向下的压力时，木块有20cm³的体积露出水面，则木块的密度约为____ $kg/m^3$。（g取10N/kg）

根据短文理解，完成下列各题。

    Helen and Linda are good friends. They are in the same class. They go to school five days a week. And they have seven classes a day. After school they play volleyball.

    The two girls' mothers are friends, too. They like sports. So they can play sports with the two girls on the weekend（在周末）. Linda's mother likes tennis and Helen's mother likes tennis, too. Can the two girls play tennis? Sure, they play it well.

    The four friends always play tennis in the morning, and watch TV in the afternoon. It's relaxing! The two girls like eating fruits. They like apples, strawberries and oranges. They think fruits are good and healthy. After playing tennis, their mothers always make (做) some fruit salad first. What good friends they are!