【题目】The conflict had developed into a stage ________ the two countries were gathering big troops on the border.
A. whereB. whichC. that D. when
在线课程【答案】A
【解析】
试题分析：考查定语从句。stage是指某事物/某人的发展、成长或进步的程度、时期或阶段。stage是先行词，在后面的定语从句中作地点状语，故选where。句意：冲突已经发展到了两国在边境集结军队的程度。