Auxiliary Verbs
We use auxiliary verbs to make negative sentences and questions. To make a negative sentence, we usually put "not" after the auxiliary verb.
They do not / don't live in London.
You should not / shouldn't smoke here.
To make a question, we usually put the auxiliary verb before the subject.
Does he have a car?
Can I open the window?
"Do", "does" and "did" are only used in negative sentences and questions. We don't usually use them in positive sentences.
The verbs "am", "is", "are" (Present Simple), and "was", "were" (Past Simple) can act as both the main verb and the auxiliary verb.
She is not / isn't my classmate.
Were you at home last night?
Some auxiliary verbs like "can", "may", "should" etc. add extra meaning to the sentence.
It may rain tonight. (possibility)
Can he play the piano? (ability)
You shouldn’t eat a lot at night. (Advice)
Exercises
Complete the sentences with the correct auxiliary verb: am, is, are, was, were, do, does, can, should, may.
1.____ you at school yesterday?
Were you at school yesterday?
2.She ____ speak German well. (not able)
She can't / cannot speak German well.
3.____ they like football?
Do they like football?
4.I ____ not feel well today.
I do not feel well today.
5.We ____ go to the park tomorrow. (possibility)
We may go to the park tomorrow.
6.____ he have a pet?
Does he have a pet?
7.You ____ eat more vegetables. (advice)
You should eat more vegetables.
8.They ____ at home now.
They are / aren't / are not at home now.
9.I ____ sorry for being late.
I am sorry for being late.
10.You ____ use your phone in class. (not allowed)
You can't / cannot use your phone in class.