What I can understand from your question, rational use suggest that you use things in a rational way or in a logical,astute,prudent way. This means, for example, you are lost in an island and you know someone is going to look for you in the following 10 days, still you dont know in which day you are going to be rescued. Because you are an inteligent human being you will decide to use your things in a rational way as if you dont do it you will have a shortage of supplies and most probably you are going to die.
-Hope this works...
Okay so the question is asking you about Nobel's brothers. Noble must have something really big or great and they are asking how his brothers helped his do what he did. They are also asking who you think helped Nobel more.
