如果把一个正方形按4：1放大，放大后与放大前边长的比是____，面积的比是____．如果把正方形按1：2缩小，则边长缩小到原来的 ____，面积缩小到原来的____．

根据短文内容，选择最佳答案。

    I come from Holland (荷兰). In our country, there are plenty of windmills. There are more than 2,000 windmills in Holland. These windmills make electricity (电) for the country. It is a small country in Europe. About 20% of its land comes from the sea. The population of Holland is only 16,000,000. The weather is very nice, so the flowers can grow very well. Maybe you like roses, kapoks or lilies. However, the tulip is a symbol (标志) of the country. People celebrate Tulip Festival every year. There are a lot of cows in this country. You can enjoy good milk and cheese here. You can go everywhere by train, taxi, underground or ship. They are fast and convenient. People here also love to ride bikes. Riding a bike is free and relaxing. What do children do when they pass their exam? They often hang a schoolbag and a national flag at the gate! Come and have a good time in Holland!

潮汐是月球、太阳对地球的引力作用而产生的．每天的涨潮与落潮蕴含着巨大的能量，这种能量可以用来发电．如图所示，在利用潮汐发电的过程中，能量的转化情况是海水的动能传递给发电机，通过发电机转化为 ____能；图中甲、乙两幅图代表涨潮发电的是 ____；与火力发电相比，潮汐发电的优点是 ____

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