如果代数式$\sqrt{a}$ +$\frac{1}{\sqrt{ab}}$ 有意义，那么直角坐标系中点A（a，b）的位置在（　）

读“西双版纳景洪市各月气温和降水量图”，完成下列要求。

根据材料内容，选择正确答案。

    Jim, a young farmer, was once put into prison (监狱).

    One day, he got a letter from his mother. "I'm so worried about our farm," she wrote. "It's time to plant potatoes. I can't dig(挖) all the fields by myself. "

    Jim read the letter and became sad. "What can I do?" he thought. Then he had a good idea. He wrote to his mother, "Don't dig the fields. There's a pot of money in the earth. Don't plant potatoes until I come home."

    Some days later, Jim got another letter from his mother. It said, "Two days ago, about ten men came to our farm and dug all our fields. I can't understand it. It looks as if they were looking for something. What shall I do?"

    Jim smiled when he read his mother's letter. He wrote a letter to his mother at once. It was very short. Guess what it would say?

在XY型性别决定的生物中，雌性个体细胞中染色体组成可用2N＝2（A＋X）表示。下列解释中，不正确的是