article: Mr Green is from England. He and his wife   are teachers. They teach English in Beijing. They have a boy and a girl. They are Jack and Mary. Jack is a student, but Mary is not. She is only four.
  They have two bikes. One is big, and the other is small. The big one is for Jack. The small one is for Mary.
  On Sundays, sometimes they are at home, sometimes they go to the park. The Greens like China. They have a lot of Chinese friends.
question: On Sundays, they are sometimes   _  .
options: at school in the classroom at home on the bike