The word order of an interrogative sentence is 1. auxiliary verb 2. subject 3. main verb 4. object. If an interrogative sentence has a question word, the question word begins the sentence:

Do you need help?

 

When does the bus leave?

The most common question words in English are: 

• what 
• which 
• why 
• when 
• how 
• whose 
• where 
• who:

Who sent you an invitation to that party?

If the interrogative sentence contains to be, the auxiliary verb do is not used:

Are you lost?

Question tags are added to the end of statements to turn them into questions. They can be used to check if something is true, or invite people to agree with us. If the main part of the sentence is positive, the question tag is negative.  If the main part of the sentence is negative, the question tag is positive:

This is an extremely cosy bedroom, isn’t it?

 

The weather isn’t going to get much better today, is it?

Question tags consist of an auxiliary verb (be, have, do], or a modal) and a subject pronoun (I, you, she/he/it, we, you, they) or a “dummy” subject there. Use the corresponding subject pronoun in the tag. If the subject of the sentence is Mark, use he. Conjugate the verb according to the person and the tense (here, the third person singular and the present tense):

Mark is staying at home today, isn’t he?

If the main part of the sentence doesn’t have an auxiliary verb, the question tag uses an appropriate form of do:

They forecast a cold period of two weeks, didn’t they?

If there is a modal verb (e.g. must, will, should, would, can, could) in the main clause, the question tag is formed with the same modal verb:

You couldn’t see I was waving at you, could you?