問題詳情
6.Those experiments were a________ stone towards two of the most importantand profitable vaccines in history: the mRNA-based COVID-19 vaccines givento hundreds of millions of people atound the world.
(A) obstructing
(B) moving
(C) putting
(D) stepping
參考答案
答案：[無官方正解]
難度：計算中-1
書單：沒有書單，新增