Last Sunday the Greens went to climb the hill. When they got home, it was very late. Mr. Green opened the front door and they both went into the house. Because it was too late, Mrs. Green turned on the light. Just they wanted to come into the bedroom, Mrs. Green suddenly said, “ Listen, there is someone in our bedroom.” They stood quietly outside the door. They could hear some voices in the room.
“There are two men in it. They are talking.” So Mr. Green began to shout. “Who is there?” But no one answered. Mr. Green opened the door quickly and turned on the light. There was no one there. Mr. Green found something and laughed. The radio was still on! “I forgot to turn it off this morning.” Mr. Green said.

从1－9这九个自然数中任取一个，是2的倍数的概率是（    ）