Auxiliary verbs.

1. Auxiliary verbs.
The verbs do, be and have are used as auxiliary verbs to form different tenses.
1. Do
a. Do as an auxiliary is used to form negative and question forms of the Present Simple and did is used in the past tenses.
I don’t understand.
Do you like it?
I didn’t agree.
He didn’t pass.
Did you enjoy your meal?
b. Do is only used in the positive to give emphasis to a verb:
She isn’t lazy. She doesn’t try hard.
I did try to phone, but there was no answer.
c. Do is in tag questions and short answer.
You think it will work, don’t you?
You don’t want to go, do you?
It worked, didn’t it?
2. Be
a. Be as an auxiliary +present participle ( ing) is used to form continuous tenses:
Alice is writing book.
We are going to for a walk.
b. Be+ past participle(ed) is used form passive sentences.
Paper is made from food.
My car is being repaired at the moment.
He was injured in a car accident
. It will be finished soon.
3. Have
Have as a auxiliary +past participle(ed) is used to form perfect tenses.
I have never been there before.
By the time we arrived they had left.