见下表，该项措施的主要意义在于（   ）

②∵ ${\left(x-\frac{1}{3}\right)}^2$ ≥0，∴ ${\left(x-\frac{1}{3}\right)}^2$ + $\frac{1}{2}$ ＞0.

模仿上述方法解答：

求证：

某风景区附近是大型的陶瓷生产基地，工厂排放的气体使景区内酸雨频频。风景区内受酸雨影响最小的是（    ）

阅读短文，完成下列问题

A five-day holiday can be very exciting for anyone. But a small thing can also make you feel really bad.

    One sunny day Mr. Li wanted to go to Hangzhou for a trip. He wanted to take a train because he would like to see the villages and rivers along the way. And it was not expensive. After he arrived at the train station, he waited for（等待）a long time. He had nothing to do, so he bought a book and read it. When the train came, he got on the train and sat down. About ten minutes later, a man came up to him and said, “Excuse me, sir. This is my seat.”

  “What?” Mr. Li said, looking at his ticket（票）.

  “Are you going to Chengdu?” the man asked.

  “No, I'm going to Hangzhou,” Mr. Li answered. And then he knew he got on the train by mistake.

   Luckily, he didn't miss the right train. All in all, it was not a good start.