问亲们英语语法问题,that的省略问题,

问亲们英语语法问题,that的省略问题,英语语法高手帮帮忙啊 关于that的省略
1当宾语从句是双宾语中的直接宾语时答：连词that可以引导宾语从句.这个that 在从句中不作成分,没有意思,常可省略.不过,如果有两个由that引导的宾语从句,用and并列起来时,前一个that可以省略,后一个不可以省略.如：He said (that) he would come and that he would help me.
如果that引导的是双宾语中的直接宾语如：He told me that he would come.这个that最好不省略,不过省略也不影响理He told me he would come.完全可以.当这个从句比较短时,就可以省略,较长时,最好不省略.
2当宾语从句的主语是非谓语动词或从句时
答：可以省略,尤其是句子较短时,如：He said (that) seeing is believing.He said (that) to see is to believe.He said (that) what I did was correct.
3当主句的谓语动词与宾语从句之间有插入语时
答：这个不能省略,因为这是个标起,需要它：He said,believe it or not,that he could fly to the moon.
4当THAT宾语从句中的状语从句位于该从句的前部时
答：最好不省略,因为省略就容易误解,不知道这状事从句是主句的还是宾语从句的.
用一下楼上的列句：
Tom promised that if he could earn as much as 500 dollars in this month,he would buy a computer for his brother.
汤姆许下诺言,如果他在这个月里能够赚到500美元,他就给他的弟弟买台电脑.
如果省略,则将从句放在宾语从句的主句后：Tom promised he would .for his brother if he could .in this month.
能不能分别举一个列子?