Why did n't you do your homework?

1. I'm sorry, but I was very tired yesterday.
2. Excuse me, but I forgot to do homework.
3. Forgive me, but I was very busy caring for my mother in hospital.
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Are the answers all grammatical? What other expressions can we use when we say 'excuse' or 'pretext'? Thank you for your help. Will you name some of them, please?

You can also say, "Pardon me, ... "

Yes, all three answers are grammatically correct. When we want to give an excuse or a pretext for not doing something, there are various expressions we can use instead of "excuse" or "pretext". Here are some examples:

1. Apology: I apologize for not doing my homework.
2. Reason: I had a reason for not doing my homework.
3. Explanation: Let me explain why I didn't do my homework.
4. Justification: I have a justification for not completing my homework.
5. Explanation: I can provide an explanation as to why my homework wasn't done.
6. Sincere apology: Please accept my sincere apology for not doing my homework.

These are just a few examples of alternative expressions you can use when giving reasons or excuses for not completing a task.