—I said hello to Mr Green, but he said nothing and just kept on walking forward.

—It's probably that he didn't hear you.

隋朝开凿大运河是在（  ）

阅读短文，完成句子。
    Lychees grow in the south (南方) of China. They are small with red peel (果皮). Most people like to eat them, because they are sweet and full (充满的) of juice.  There is an old story about lychees. Yang Yuhuan loved lychees very much. Lychees have a lot of vitamin C. It is very important for people. Vitamin C can make children more healthy. So many parents often buy lychees for their children. Amy and her mum are in the fruit shop now. What fruit are they going to buy? Look! They are buying lychees
从文章中找到适当的单词或短语填空，完成句子。

计算178－156÷12×13时，要先算____法，再算____法，最后算____法．

下列属于种群空间特征的描述的是（    ）。