阅读下面材料，在空白处填入适当的内容（不多于3个单词）或括号内单词的正确形式。
He was a professor. At the age of 90, he still worked eight hours every day regardless            the weather.
His secretary said: “He was extremely old, but he forced himself to walk from his living place to the office through two blocks.       would take him an hour to do so, but he insisted because it made him get a sense of        (succeed).”
One day, a university student       (step) out of his office with a pile of books. He complained: “He always answers my questions with just a yes or no. However, he always gives me dozens of books and suggests me       (find) the answer on my own.”
By chance, the professor knew        the student complained about. He explained to him with a smile: “This is the method I have learnt---the       (hard) you work independently, the better solutions you will find. If you can make full use of the books, you will       (probable) become a good lawyer in the future.”
This 90-year-old man was Pound,         was the president of Law College of Harvard. He believed “all slopes are easy     ( go)”, of which he often reminded his students.