Read the following passage, and choose the correct answer to each of the questions

    In order to learn to be one’s true self, it is necessary to obtain a wide and extensive knowledge of what has been said and done in the world : critically to inquire into it,nearly to sift it, and earnestly to carry it out .It matters not what you learn ,but when you once learn a thing, you must never give it up until you have mastered it.It matters not what you inquire into, but when you inquire into a thing, you must never give it up until you have completely understood it .It matters not what you try to think out, but when you once try to think out a thing , you must never give it up until you have got what you want . It matters not what you try to sift out ,but you once try to sift out a thing, you must never give it up until you have sifted it out clearly and distinctly .It matters not what you try to carry out , but when you once try to carry out a thing , you must never give it up till you have done it completely and well . If another man succeeds by one effort, you will use a hundred efforts.If another man succeeds by ten efforts, you will use a thousand efforts. 

According to the author the ultimate purpose of study is to learn to ________ .