求英语句子找错

题目

求英语句子找错
不要求改正 只要告诉我为什么错了.
1.Among the dicoveries made possible by the invention of the telescope they found that dark spots existed on the Sun in varying numbers.
为什么“they found”错了?
2.Norwegian writer Sigrid Undset is like the novelist Sir Walter Scott in her use of historical backgrounds,but unlike his books,she dwells on the psychological aspects of her characters.
为什么“his books”错了?

答案

1.they had found 过去完成进行时,表示动作发生在过去时的前面
2.his books 应该改为 him