These signs are not very difficult to see them.为什么去掉them

These signs are not very difficult to see。就正确的句子来看,句子的结构已经非常完整了,these signs 是句子的主语,see是动词,可以试图将句子改写为：It is not very difficult to see these signs。就很明显看到them是多出来的部分 以后可以尝试用这个方法做题