1. They didn't have green leaves yet.
2. She didn't finish her homework yet.
3. He didn't clean the room yet.
4. She didn't read the book yet.
(Are all the sentences grammatical?)
3 and 4 would read better with "hadn't cleaned" and "hadn't read," but as they're written, they are not incorrect.
Yes, all the sentences are grammatically correct. They follow a common structure in English known as the negative form of the past simple tense. This form is used to express actions that did not happen in the past, or actions that were not completed by a certain point in the past. The word "yet" is often used in negative past simple sentences to indicate that the action has not happened up until now.
To check the grammaticality of these sentences, you can analyze the structure of each sentence. In each sentence, the subject is followed by the auxiliary verb "did" in its past tense form, and then the base form of the main verb. The word "yet" is placed at the end of each sentence after the verb.
1. They didn't have green leaves yet.
2. She didn't finish her homework yet.
3. He didn't clean the room yet.
4. She didn't read the book yet.