How do you say “I don’t know” professionally?

How do you say “you’re wrong” politely?

How do you say “I don’t know” more casually in English?

Auxiliary Verbs Quiz: Be, Do, Have

Auxiliary Verbs Quiz: Be, Do, Have

Auxiliary Verbs Quiz: Be, Do, Have

Auxiliary Verbs Quiz: Be, Do, Have

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Choose the correct answer.

Very sorry to ask native English speakers for help but very much thank you/them ( sorry I don't know whether I use the word "them" or "you" to refer to "native English speakers here) The following are all simple sentences related to concessive clause, but which make be at a loss in understanding which is grammatically correct. 1a. Children that they were, they knew what was the right thing to do. 2. Children that they were, they knew what the right thing to do was. 3. Child that he was, he knew what was the right thing to do. 4. Child that he is, he knows what was the right thing to do. 5. Naked man that I was, I braved the storm. 6. Naked men that they were, they braved the storm. 7. Child as/though he is, he is two meters tall. 8. Clever though the child is, he is two meters tall. 9. Clever as he was not, the man could solve that complex problem. 10. Clever that he was not, the man could solve that complex problem. 11. More clever as he was, he still did not solve the mystery. 12. They solved very difficult problem, very clever that they were. 13. They still did not solve the very difficult problem, clever that they were not. Question: Which is grammatically correct?