Knowledge from real life isn't easier to forget than achieved from textbooks．
A. it
B. that
C. one
D. those
网友回答
A. it
(答案→)B. that
C. one
D. those
解析：考察代词用法。It指代上文提及的同一事物；that指代可数名词复数或不可数名词，后面要有定语限定，those是其复数形式。One指代上文提及的可数名词单数.根据句意可知本题that代替不可数名词knowledge.