As far as I know, it is a terrible mistake to use "that" after the comma. As it is a non-defining relative clause, one may only employ "which".

Thanks for your answer, Clive. Taking into account the examples you give, it seems to me (but I may be wrong) that my sentence looks more like the second one.

While "googling", I found both usages. Though I know that this doesn't mean that both are correct.

I suppose that, if you want to add something, you must use "have been". In any case, I think the sentence is correct and clear enough without it.

I suppose that from (a) we know that I have at least one copy of the report, but in any case (c) is definitely the correct answer.

This thread has its origin in a previous where I posted the following paragraph: "I employ the term 'dogmatist' in the sense in which S. uses dogmatikos , namely, to designate someone who makes positive or negative assertions about the nature

Mmm, I don't really see what the problem is.

Hence, I could say: "I employ the term 'dogmatist' in the sense in which S. uses dogmatikos , namely, to denote someone who makes positive or negative assertions about the nature of things, on the basis of what he considers to be evidence and

Thanks for your answer; you're right: I should use "a person". In any case, after rereading the second alternative, the combination of "a person" and "that person" in the same sentence just sounds ungainly to me.

Pinenut, it seems to me that your argument clearly proves what I said. But then, does it sound ok if I say "that that which .... that that which" ?