已知酒精、煤油、水银的熔点分别为－117℃、－30℃、－38.8℃，南极的最低气温可达-89.2℃，要测量南极的气温，应该选用（     ）

植物生长需要量最大的是含____ 、____ 、____ 的无机盐。

    An old porter (搬运工人) had worked for the railway for a very long time. One morning he was standing in one of the big railway stations and waiting for travelers to ask him to help them with their luggage, when he saw a small man running toward the trains with a big bag in his hand.

    The porter watched the man for a few seconds, and the man saw the porter.

At once the small man ran up the porter and said, "Can I catch the 10：35 train to London, porter?" He was breathing very fast, and he seemed worried.

    The old porter looked at him for a moment and then said with a smile, "Well, sir, I'd like to help you, but I can't answer your question because I don't know how fast you can run along rails. You see," he explained, "the 10: 35 train to London left five minutes ago."