on后面加什么?

例句：

We were on a hill, right on the edge of town.

我们在一座小山上，正好位于城镇边缘。

What's on TV?

电视上有什么节目？

Two men riding on motorcycles opened fire on him.

两个骑在摩托车上的人向他开了枪。

His eyes lingered on the diamond ring on her finger.

他的'目光滞留在她手指上的钻戒上。

I'm forever on a diet, since I put on weight easily.

我一直在节食，因为我的体重很容易增加。