补充128

128.       During the Renaissance, scholars were uncertain as to the location of Troy, and by the eighteenth century many historians doubted that Troy had ever existed.

(A) doubted that Troy had ever existed

(B) doubt that Troy has ever existed

(C) were in doubt as to the existence of Troy

(D) were doubtful concerning Troy’s existence（A）

(E) had doubts about Troy’s ever existing

我选了e。因为看到前面的那个by the eighteenth century， 中学老师就教给我们 by。。。时间为至，后面用完成时。不对么？

by the eighteenth century 是表示过去的时间概念，而且句中没有表示以动作发生与另一过去的动作之前，所以不能用过去完成时，而用过去时。