阿摩線上測驗
55 The plane cannot leave the gate ___ all passengers are seated and baggage is safely stowed.
(A)but
(B)if
(C)unless
(D)when
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統計： A(3), B(6), C(87), D(9), E(0) #867384
統計： A(3), B(6), C(87), D(9), E(0) #867384
