This story is about a young man. He worked hard at his lessons. He was too busy. He didn’t have time to rest, so he was ill. Every night, when he went to bed, he closed his eyes and tried to sleep（睡觉）. But he couldn’t. He thought: “I must go to see the doctor.” He said to the doctor. “I can’t go to sleep at night.” “Try counting numbers. When you reach one thousand, you’ll be asleep.” The next day the man came back to the doctor’s office. “Well,” said the doctor, “How are you today?”“Yes, he said,” I tried counting one, two, three. . . up to （直到）one thousand. But when I reached five hundred and sixty-nine, I began to feel sleepy (感到困倦). I had to get up and drank some tea. Then I went on counting up to one thousand. But I still couldn’t fall asleep.

①三角形的直观图是三角形；

②平行四边形的直观图是平行四边形；

③正方形的直观图是正方形；

④菱形的直观图是菱形．

以上结论，正确的是（   ）

植物细胞分裂的顺序是（  ）

①细胞质分成两份，每份含有一个新的细胞核；

②细胞核分裂成两个新的细胞核；

③母细胞中央形成新的细胞膜和细胞壁．

我国西北内陆地区干旱的自然特征形成原因多样，干旱本身就包含荒漠化的潜在威胁。据此完成下列各题。