这里的on是副词，意思是指“在进行中”。如：

The strike was on. 罢工正在进行。

The convention was on. 大会还在开。

Richard I is on again. 《理查德一世》又在上映了。

Breakfast is on from 8 to l0. 八点至十点之间开早饭。

She knew something was on. 她知道什么事正在发生。

What’s on at the Capital Theatre? 首都剧场演什么戏?

The film was already on when we arrived. 我们到时, 电影已经开演了。

The strike has been on now for six weeks. 罢工至今已进行六个星期了。