These words are verbs and can have several functions. Can and could, and will and would, have similar meaning but they have subtle differences.

In this programme, Rob and Li look at which words you can use in which situation. Sometimes it depends if you are talking about the past or the future and sometimes it's a question of politeness or formality.

What is the difference between these two statements? Listen to the programme to check whether you are right.

1. When I was young I could run fast.

2. I am old and I can only walk to the bus stop.

If you have a question for our team, send it to us at questions.chinaelt@bbc.co.uk and we might answer it on this programme.