I have a question about conjunctions, dependent and independent clauses.
The issue came up when a text book suggests that "and it" can replace "which/who". But my understanding is that subordinating conjunctions are used for connecting dependent clauses, whilst coordinating conjunctions are used with independent clauses.
So here are some examples.
This book is about King Sejong, who invented Hangeul. This book is about King Sejong and he invented Hangeul. No.1 to me is correct whilst 2. isn't.
Another example however
The word shampoo comes from the Hindi word champo, which means "to press". The word shampoo comes from the Hindi word champo and it means "to press". In this case, both look correct to me.
In the 1st example, is it incorrect because the subordinate clause acts as a adjective clause, whilst the 2nd example isn't?
One final example that is obviously wrong:
I am reading a book about Paris, which I visited two years ago. I am reading a book about Paris and I visited two years ago.
I tried asking on English Stack Exchange but only received one comment saying
"The whole point of having relative clauses is to avoid having to use your examples with "and""
But no clear explanation on the exact grammar at play which allows some cases to be okay whilst in others, not.
Is there a grammar mistake in the wrong sentences? Or is it just semantically unclear?