“你是我的对手，但不是敌人，因为你的竞争给予我力量”，这告诉我们（   ）

中国在新工业化发展过程中，开发可再生能源以缓解石油短缺引起的能源危机是一个重要的课题.2003年元月份，某省投资建设一个年生产工业酒精500万吨的工厂，目的是为了将工业酒精与汽油混合作为汽车燃料而减少汽油的消耗量．已知制酒精的方法有三种：

方法一：CH₂=CH₂+H₂OCH₃CH₂OH

方法二：CH₃﹣CH₂Br+H₂OCH₃CH₂OH+HBr

方法三：（C₆H₁₀O₅）n（淀粉）+n H₂O  n C₆H₁₂O₆（葡萄糖）

C₆H₁₂O₆（葡萄糖） 2C₂H₅OH+2CO₂↑

    John was a kind man. When he was young, he hoped ____(become) a singer. But he didn't have enough money ____ (buy) books about music. And his parents didn't expect him ____ (be) a singer. So his dream didn't come tree. At the age of fifteen, he ____ (leave) his village and found a job in a small town. He worked there for five years. Later his mother became very ill (生病的) and he had to ____ (stop) his work to come back and look after (照顾) her. Three years later his mother died and he wanted to leave his village again and  ____ (work) in other places. However, John couldn't. His father was ill. John decided____ (stay) at home and look after him. Every day he ____ (do) many things for his father. Day by day, John became old. But he still didn't forget his dream to be a singer. Now he has lots of time so he plans to learn to sing at a music school.

甲：根据一个数的平方是非负数可知（a﹣b）²≥0，

∴a²﹣2ab+b²≥0，

∴a²+b²≥2ab．

乙：如图1，两个正方形的边长分别为a、b（b≤a），如图2，先将边长为a的正方形沿虚线部分分别剪成Ⅰ、Ⅱ、Ⅲ三部分，若再将Ⅰ、Ⅱ和边长为b的正方形拼接成如图3所示的图形，可知此时图3的面积为2ab，其面积小于或等于原来两个正方形的面积和，故不等式a²+b²≥2ab成立．

则对于两人的作业，下列说法正确的是（   ）