为什么用what？不用which、that？

The two farmers carrying what appeared to be small guns forced the enemy officer to hand in his map.
what在从句中作主语吧？可以顺便帮我翻译一下。

The two farmers carrying what (=something that) appeared to be small guns forced the enemy officer to hand in his map.
两名农夫携带着似乎是小型枪械的东西，逼迫敌人军官交出了地图。

though the story of liyunlong in the tv drama "bright sword "is a fiction ,much of what happened is historically true. 帮助翻译这个句子，并且解释为什么不用which而用what

what在这引导一个从句，做carry的宾语。主语可以简化为the farmer，后面一直到forced全是修饰the farmer的，也就是定语。完整的是 the farmer that carried……

what主语从句、庄稼汉）来干。 what appeared to be small guns，带着象是小枪一样的东西两个地主，因此是庄园主，carrying后面如果有arms（武器），雇用peasant（农民，不是一般农夫、农场主，这时才能用which或that构成定语从句，逼迫敌方军官交出了地图，至少富农。 farmer有很多地，大多不干活或只干一点