Originally I choose D.
The answer key says "Past perfect “had been” cannot be used in the absence of another past tense event."
^can someone explain this further?
Can someone explain/show how "D" could be the right answer? Ex. with a past tense event
Question: Biologists worry that the Arctic ecosystem will unravel quickly, citing the fact that the average temperature within the Arctic circle is already two degrees warmer than ten years ago.
The answer key says "Past perfect “had been” cannot be used in the absence of another past tense event."
^can someone explain this further?
Can someone explain/show how "D" could be the right answer? Ex. with a past tense event
Question: Biologists worry that the Arctic ecosystem will unravel quickly, citing the fact that the average temperature within the Arctic circle is already two degrees warmer than ten years ago.
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