阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。

    Many American presidents were born in poor families. They (spend) their childhood in wooden (木制的) rooms. They got little (educate). Washington and Lincoln, for example, never went to school. They taught (them). Lincoln once did jobs as a worker, a shopkeeper a post officer in his early   (year). Besides, a number of US presidents had experiences in the army, such as Grant and Eisenhower. Grant was general (将军). It (happen) that they came from same school—West Point Military Academy (西点军校). However, these (difficulty) experiences had a great effect their life and helped them succeed.