7. According to IGC Code, self-contained breathing apparatus shall have at least a duration of service of __________ minutes.
(A) 10
(B) 15
(C) 20
(D) 30
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統計: A(102), B(409), C(61), D(194), E(0) #2929010
統計: A(102), B(409), C(61), D(194), E(0) #2929010