comma to link separate, yet related clauses?

0Hi,02br
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00I think you can use a comma to sort of link two separately written, yet very related-in-content clauses like this:02br
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01i00Thank you, it was good to receive a gift of appreciation by you last week.02i02br
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00I think 'Thank you' and what follows can be thought of as two separate clauses yet can be linked by a comma.02br
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01i01u00That was his decision02u00, deciding to support his care his aged father by himself and not put the father somewhere difficult to care for was the right thing to do. -- Since the underlined clause contains an element, which is 'decision'. that is further elucidated by the longer clause that followed, I think it could be argued a comma is correclty used. Right?02i02br
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01i00But you wouldn't agree this use of a comma is correct, would you?02i02br
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01i01u00That was thrown abruptly02u00, he could not have anticipated its coming while quite immersed in his conversation with his old friend. -- 'it' refers to a ball, in this case.02i02br
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00Are there a guideline as to this use of comma (if it is in fact correctly used)? 0-