article: Xiao Ming  is playing with his friend in front of a house. An old woman walks up to him. "My boy," she asks., " Is your mother at home?" "Yes ," Xiao Ming says. The woman begins to ring  the door bell , but there is no answer .
  She rings the door bell again. There is still no answer. The woman is not happy. She turns to Xiao Ming  and asks again, "Is your mother at home?" "Yes , she is." Xiao Ming  answers. "But I ring the door bell twice and nobody  comes to open the door," the woman says.
  "Oh, I'm sorry. This is not my house. My house is over there."
question: Xiao Ming's mother is   _  .
options: at work at home at school out