Question

Select the correct relative pronoun to complete this sentence.

Answer 1

The correct relative pronoun to complete this sentence.

Alchemists​,​ _____ wanted to transform base metals into​ gold, were also among the first people to conduct laboratory​ experiments is option D. WHO

It is a non-defining realtive clause. Non-defining realtive clauses add extra information to a sentence by defining the noun. That can be used as a replacement of which or who in defining relative clauses.  But it is not correct to use THAT to replace shich /who in non defining realtive caluses