阿摩線上測驗
6.Those experiments were a ________ stone towards two of the most important and profitable vaccines in history: the mRNA-based COVID-19 vaccines given to hundreds of millions of people around the world.
(A) obstructing
(B) moving
(C) putting
(D) stepping
(A) obstructing
(B) moving
(C) putting
(D) stepping
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統計： A(3), B(1), C(3), D(4), E(0) #3024586
統計： A(3), B(1), C(3), D(4), E(0) #3024586
