Food is very important. Everyone needs to____  well if he or she wants to have a strong body(身体). Our brains (大脑) also need a kind of food. This kind of food is ____ . We begin to get knowledge (知识) When we are very young. Small children are interested in everything around them. They learn ____  while (当) they are watching and ____ . When they are getting older, they begin to ____  storybooks, anything they like. When they find something new, they like to ask questions and ____  to find out the answer.
What is the best ____  to get knowledge? If we ____  by ourselves, we’ll get the most knowledge. If we're ____  getting answers from others and do not ask why, we will never learn well. When we study in a right way, we will learn ____  and understand (理解) better.

“向       同志学习。憎爱分明的阶级立场，言行一致的革命精神，公而忘私的共产主义风格。奋不顾身的无产阶级斗志。”的题词中的空格处应为（  ）

怎么简便就怎么算．

(4＋0.4)×2.5－7.3

 某校同学以“比较锰、铁、铜3种金属的活动性”为课题进行探究。
提供的药品：铁片、铜片、锰片、稀盐酸、硫酸亚铁溶液、硫酸铜溶液、硫酸锰溶液。
【做出猜想】他们考虑到铁的活动性比铜强，对3种金属的活动性顺序作出如下猜想。
猜想一：锰>铁>铜；猜想二：铁>铜>锰；
猜想三：____ 。
【设计实验】为了验证猜想成立，同学们分成三组，分别针对一种猜想设计实验方案。
（1）第一组验证猜想一。实验方案是将锰片、铁片分别放入稀盐酸中，观察现象。
（2）第二组验证猜想二。实验方案是将锰片放入____ 中，观察现象。
（3）第三组验证猜想三。实验方案是（只用两个实验）：____ 。
【实验及结论】各组通过实验和交流，确认猜想一是正确的。第一组同学的实验现象是：____ 。
【拓展探究】随后同学们对探究金属活动性的方案设计作了进一步研究。
为了验证甲、乙、丙、丁4种金属的活动性依次减弱，某同学设计了如下方案：①把甲放入乙的化合物溶液中；②把乙放入丙的化合物溶液中；③把乙放入丁的化合溶液中；④把丁放入丙的化合物溶液中。你认为哪个实验没有必要做？请说明理由。____ 。