（2015·茂名）阅读下面文章，根据文章内容，从每小题所给出的A、 B、 C、 D四个选项中选出最佳答案

One morning, Mr Black was driving in the country and looking for a small hotel. When he saw an old woman on the side of the road, he stopped his car and said to the old woman, “I want to go to the Sun Hotel. Do you know it?”

“Yes,” the old woman said,“I will show you the way.” She got into Mr Black’s car and they drove about twelve miles. When they came to a small house, the old woman said, “stop here!” Mr, Black stopped and looked at the house.“But this isn’t a hotel.” He said to the old woman.

“No”the old woman answered, “This is my house. And I'll show you the way to the hotel. Turn round and go back nine miles. Then you’ll see the hotel.”

①体温恒定  ②变温动物  ③胎生、哺乳  ④体表被毛  ⑤属于先天性行为  ⑥属于学习行为

我国的南海资源丰富，其面积为3500000平方千米，相当于渤海、黄海和东海总面积的3倍．其中3500000用科学记数法可表示为____．