The Whites had thought that we would visit the Summer Palace but we didn’t have enough time then.
答案 是 C had thought ,would visit
根据后句 判断 句子是过去时 排除 AD
第一句主句谓语 发生 在 第二句 谓语 之前 所以用过去完成时 排除B
所以 答案是C