113 Our research team _____ on developing a more efficient battery for the past two years.
(A) works
(B) is working
(C) has been working
(D) worked
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統計: A(27), B(57), C(895), D(122), E(0) #3772621
統計: A(27), B(57), C(895), D(122), E(0) #3772621