A. The researchers, who are experts in the field, they presented findings at the conference.
B. None of these
C. The researchers who are experts in the field, presented findings at the conference.
D. The researchers, who are experts in the field, presented findings at the conference.
Explanation
The sentence is a complex sentence, containing an independent clause ("The researchers...presented findings") and a dependent clause ("who are experts in the field").
The commas correctly set off the dependent clause, providing clarity and proper punctuation.
