下列一组单词中，划线部分发音不同于其它三个的单词是_______。

Nowadays people attach importance _______ the children’s pre-school education

In my opinion, life in the twenty-first century is much easier than _______

Tom’s father____ to London last month. He ______ there three times.

The old man has____useful horse and horsecan do a lot of things for him.