There are two verbs in each of these sentences:
I have lost my keys.
She can’t come to the party.
The hotel was built ten years ago.
Where do you live?
In these examples have/can’t/was/do are auxiliary (= helping) verbs.
You can use an auxiliary verb (without the rest of the sentence) when you don’t want to repeat something:
* ‘Have you locked the door?’ ‘Yes, I have.’ (= I have locked the door)
* George wasn’t working but Janet was. (= Janet was working)
* She could lend me the money but she won’t. (= she won’t lend me the money)
* ‘Are you angry with me?’ ‘Of course I’m not.’ (= I’m not angry)
Use do/does/did for the present and past simple:
* ‘Do you like onions?’ ‘Yes, I do. (= I like onions)
* ‘Does Mark smoke?’ ‘He did but he doesn’t any more.’
We use have you?/isn’t she?/do they? etc. to show polite interest in what somebody has said:
* ‘I’ve just met Simon.’ ‘Oh, have you? How is he?’
* ‘Liz isn’t very well today.’ ‘Oh, isn’t she? What’s wrong with her?’
* ‘It rained every day during our holiday.’ ‘Did it? What a pity!’
Sometimes we use these ‘short questions’ to show surprise:
* ‘Jim and Nora are getting married.’ ‘Are they? Really?’
We use auxiliary verbs with so and neither:
* ‘I’m feeling tired.’ ‘So am I’ (= I’m feeling tired too)
* ‘I never read newspapers.’ ‘Neither do I’ (= I never read newspapers either)
* Sue hasn’t got a car and neither has Martin.
Note the word order after so and neither (verb before subject):
* I passed the exam and so did Tom. (not ‘so Tom did’)
You can use nor instead of neither:
* ‘I can’t remember his name.’ ‘Nor can I’ or ‘Neither can I’
You can also use ‘…not… either’:
* ‘I haven’t got any money.’ ‘Neither have I’ or ‘Nor have I’ or ‘I haven’t either.’
I think so/I hope so etc.
After some verbs you can use so when you don’t want to repeat something:
* ‘Are those people English?’ I think so.’ (= I think they are English)
* ‘Will you be at home tomorrow morning?’ ‘I expect so.’ (= I expect I’ll be at home..)
* ‘Do you think Kate has been invited to the party?’ ‘I suppose so.’
You can also say I hope so, I guess so and I’m afraid so.
The usual negative forms are:
I think so/I expect so -> I don’t think so/I don’t expect so
I hope so/I’m afraid so/I guess so -> I hope not/I’m afraid not/I guess not
I suppose so/I don’t suppose so or I suppose not
* ‘Is that woman American?’ ‘I think so./I don’t think so.’
* ‘Do you think it’s going to rain?’ I hope so./I hope not.’ (not ‘I don’t hope so’)