John, who is always idle, was punished.

John is always idle固执. John was punished惩罚. (who)

The baby, who had been disturbed by the cat, wailed loudly.

The baby had been disturbed （被打扰）by the cat. The baby wailed (大哭）loudly.

I heard some news that astonished 惊艳 me. 

I heard some news新闻. It astonished 惊艳 me. 

The rope, which was old, snapped.

The rope绳子 was old. It snapped 突然折断. （which）

We don’t like to read stories that have sad endings.

We don’t like to read stories. They have sad endings. （that）

Rebecca, whose mother is a policewoman, is my best friend.

Rebecca's mother is a policewoman. She is my best friend. (whose)

The girl, whose doll was snatched away, started to cry.

The girl's doll was snatched away. She started to cry. (whose)

The shoes, which my mother bought, were expensive.

The shoes were expensive. My mother bought it.

The shoes were expensive. My mother bought it.