Eg.

1. Regarding the issue you have been worrying, I suggest you just take it easy.

2. About the issue you have been worrying, I suggest you just take it easy.

3. As regard the issue you have been worrying, I suggest you just take it easy.

4. Referring the issue you have been worrying, I suggest you just take it easy.

5. With reference to the issue you have been worrying, I suggest you just take it easy.

6. Referred to the issue you have been worrying, I suggest you just take it easy.

7. Concerning the issue you have been worrying, I suggest you just take it easy.
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Question

a. Are the the beginning words in the above sentences are interchangeable with identical meaning?

b. Any other substitutes?

c. I know what is verb, adjection, noun, subject. Then what do we call the beginning words of the above sentences?
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