Clearly 'C'.
Archaeologists have discovered that, over five thousand years ago, Mesopotamian cooks were preparing chicken with coriander and tamarind, just as Egyptian cooks are still doing today.
(A) Over five thousand years ago, archaeologists have discovered that
We are talking about archaeologists in ourdays, not about arch in past. WRONG
(B) Over five thousand years ago, archaeologists had discovered that
We are talking about archaeologists in ourdays, not about arch in past. WRONG
(C) Archaeologists have discovered that, over five thousand years ago,
Clear and concise. THE WINNER.
(D) Over five thousand years ago, as archaeologists have discovered it,
Distorts the meaning. years ago should be closer to Mesopotamian. WRONG
(E) Archaeologists have discovered, over five thousand years ago, that
Same reason as in A and B. WRONG.