stepping lightly and heavily alternately

例句：

1. 1. She steppedout of the house and went for awalk in the park.
   她走出房子，去公园散步。
2. 2. The hikers had tostep over the stream to reach the summit.
   登山者不得不跨过小溪才能到达山顶。
3. 3. He stepped into the room withhis hands behind his back.
   他手背在身后走进房间。