One day, a boy and a girl went to the park. They saw a big tree with a swing. The swing had a big knot in the rope. The boy said, "Let's play on the swing!"
The girl said, "Yes, but we need to fix the knot first." They tried to untie the knot, but it was not fair. The knot was too tight. They pulled and pulled, but the knot did not come loose.
Just then, a big dog came to the park. The dog saw the knot and bit it. The knot came loose! The boy and the girl were very happy. They said, "Thank you, dog!" Now they could play on the swing all day.
