Sue is going to school on foot.
Mike is riding his bicycle to school.
Sue is going to school on foot, but Mike is riding his bicycle to school.
The boat hit a big rock.
The boat sank to the bottom of the river.
The boat hit a big rock, and it slowly sank to the bottom of the river.
When the boat hit a rock, it slowly sank to the bottom of the river. All of those trees will be cut down.