12.________ in Africa as a volunteer, she understood the real impact of poverty.
(A) Have been working
(B) Having worked
(C) Had working
(D) Had been working
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統計: A(30), B(197), C(42), D(175), E(0) #2982909
統計: A(30), B(197), C(42), D(175), E(0) #2982909