Look at the following sentence, please.
During free fall, (which is up to a fall minute,) a skydiver will fall at a constant speed of 20 m.p.h.
1- What is the part in the parentheses? Is it an appositive? If not, what is it?
It's simply a relative clause that the writer has chosen to put in parentheses.
2- Can I use (it is) instead of (which is)?
You COULD but even put in parentheses, it sounds waaaaaaay more natural to use 'which'. Remember, non-restrictive relative clauses are used to give extra information. Perhaps this is why an "it is" sounds strange.
Thank you all
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