楼上的可能搞错了答案是A这个地方是虚拟语气中对过去假设的 特殊用法，完整的应是what would have happened if Bob had walked farther, as far as the river bank?从句用过去完成时态，主句用would have done 的形式。出于强调条件从句的内容，从句形式可以（省略If再倒装）改为如题选项A，所以记得省略if得倒装eg.；I would not have succeeded in doing that had not for your help~~不要被后面那部分迷惑了，as far as the river bank 是说明那个farther的，分析时可
