After a lot of very serious, expensive and ________ laboratory research involving, for instance, telomeres in the chromosomes of certain cells, scientists have ________ there is a link between stress and aging.

The first blank must be in tandem with 'serious' and 'expensive'. Hence, 'arcane' and “esoteric” are synonyms; meaning understood by only a few, fits our prediction for first blank. “prorogued” means postponed, hence would not give sense to the sentence, as scientists have discovered something. Hence, (4) is the answer.