I hope that the little ----- I have been able to do does goo

这里没有答案,答案应该是 that,先行词为the little.
little 在这里是不定代词,和all 等词一样,被定语从句修饰时关系代词不能是which,而应该是that
I hope （主句主谓语）that the little宾语从句主语）【that】I have been able to do（修饰主语little的定语从句） does（宾语从句的谓语） good to them all（从句双宾语）.
全句意为：
我希望我的微薄之力能对他们所有的带来好处
再问： 如何判断是否句子的一个部分是否为插入语啊，比如我上面那句中的I have been able to do和He often helps the students who he thinks are not quick at their studies中的he thinks，为什么第一句不是插入语第二句是插入语啊？怎么区别？
再答： 插入语是可要可不要的， 可是此句中that I have been able to do 如果没有， the little 就不知所云了。再说插入语也无需一个关系词来引导。 He, I think(插入语,前后要有逗号和句子隔开）， is an actor.