RULES FOR
QUESTION TAGS:
In simple present or past tense, if there's no auxiliary verb, use "do/does/did".
Example: You like pizza, don't you?

Let's see usage of question tags in some sentences.

SENTENCE 13:
Let's go for a walk.
(Add a question tag)

ANSWER IS:
Let's go for a walk, shall we?

RULES:
Suggestive sentences often take 'shall we?' as question tag irrespective of the sentence being positive or negative.

SENTENCE 14:
Nothing has happened.
(Add a question tag)

ANSWER IS:
Nothing has happened, has it?

SENTENCE 15:
You must remember to lock the door.
(Add a question tag)

ANSWER IS:
You must remember to lock the door, mustn't you?

SENTENCE 16:
Don't be late.
(Add a question tag)

ANSWER IS:
Don't be late, will you?

RULES:
Imperative sentences (commands or requests) use question tags to seek agreement or confirmation.

SENTENCE 17:
Everybody was tired.
(Add a question tag)

ANSWER IS:
Everybody was tired, weren't they?

RULES:
Everybody is considered plural. So in agreement, question tag verb is 'weren't'.

SENTENCE 18:
I am a good student.
(Add a question tag)

ANSWER IS:
I am a good student, aren't I?

RULES:
We don't say 'aimn't I'. It's an IRREGULAR question tag. Exception to the rule.