28. One of the main causes of dust explosion is large amounts of flammable dust_____ in the air.
(A) transacted
(B) relayed
(C) suspended
(D) diluted
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統計: A(35), B(53), C(157), D(86), E(0) #3414321
統計: A(35), B(53), C(157), D(86), E(0) #3414321