seagull According to the scientists, If you're referring to specific scientists, keep the definite article. Otherwise, drop it. For the second part of the sentence, I would simply say, " ...
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seagullAccording to the scientists,If you're referring to specific scientists, keep the definite article. Otherwise, drop it.
seagullHow about (A) and (D)? Does either of them sound very unnatural?"In the world" is redundant in A, and D is unnatural.