如果她们在黑暗中再走远一点那么她们必然会掉进坑内该句用的是虚拟语气表示过去可能发生的情况
If they had gone a little further in the dark, they would surely have fallen into the pit. This sentence uses the subjunctive mood to indicate what might have happened in the past
以上为机器翻译结果，长、整句建议使用 人工翻译 。