A. as they play vital roles in maintaining ecological balance B. they play vital roles in maintaining ecological balance C. play vital roles in maintaining ecological balance D. from playi
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Mark the letter A, B, C, or D on your answer sheet to indicate the correct option that best fits each of the numbered blanks from 18 to 23.
as they play vital roles in maintaining ecological balance
they play vital roles in maintaining ecological balance
play vital roles in maintaining ecological balance
from playing vital roles in maintaining ecological balance