这道题考什么语法点啊？

古西西

For at least two decades or more previous to when the Venetian artist Giovanni Battista Tiepolo died in 1770, he was the most admired painter in Italy.
A.For at least two decades or more previous to when the Venetian artist Giovanni Battista Tiepolo died in 1770, he was
B.For at least two decades before the Venetian artist Giovanni Battista Tiepolo died in 1770, he had been
C.For at least two decades or more before the Venetian artist Giovanni Battista Tiepolo's dying in 1770, he had been
D.When the Venetian artist Giovanni Battista Tiepolo died in 1770, for at least two decades previously he was
E.When the Venetian artist Giovanni Battista Tiepolo died in 1770, having been for at least two decades befor

正确答案是B，我选择的A，我不明白这里为什么是过去完成时
C的所有格+ing错了
其他的都错哪了？

栖叶泠风

at least已经表明了至少，所以more previous(这个更拗口了), more before就显得很多余。
句子的意思是，在他死之前，他曾####，所以是过去完成。

falco

在挂掉之前的20年或者更早，这位仁兄都是最牛X的画师。这不就是过去的过去吗？不用过去完成时用啥？你告诉我~~