Tag questions (short answer) in declarative sentences:
A tag is formed by taking the helping verb of the main verb (make it a question to find the helping verb).
Everybody forgot to congratulate her.
Did everybody forget to congratulate her?
TAG: Everybody forgot to congratulate her, didn't they?
Main verb: forget Tense: simple past (forgot).
Also, don't forget that in a declarative sentence tag, the tag must be negative interrogative (didn't they?). In a negative sentence, the tag must be plain interrogative (They didn't forget to congratulate her, did they?).
You can practice with these:
The boys have found the dog and brought him home. [tricky, kind of]
You will be going to school this afternoon.
We wouldn't have been in town so late, normally.
Clues: the helping verbs are either in the sentence (have, will, is/are, would/should) but in the present and simple past, you have to come up with [do/does and did).
You speak Russian, don't you? You have to remember that do is the helping verb.
This is just a basic introduction, not the whole entire story.
Here is an important irregularity:
I'm being clear, aren't I? :) [regular]
VERSUS I'm being clear, am I? [in response to praise or to be sarcastic, for example]
That one does not follow the rules, you just have to learn it. First person sentence in the present tense with a tag.
Also, in a negative sentence: I'm not being clear, am I?