18. The smoke from wildfires can become a major ________ that leads to air quality deterioration.
(A) premise
(B) hazard
(C) hoax
(D) scam
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統計: A(44), B(495), C(69), D(30), E(0) #2673780
統計: A(44), B(495), C(69), D(30), E(0) #2673780