1. Taking a book off the shelf he soon found himself absorbed, not by the words of the book, but by the notes penciled in the margin.

此句现在分词作状语表示伴随还是原因？

既不是伴随，也不是原因。从书架上取下书和看书被吸引是两个紧密衔接的动作，因此可以理解为时间状语，”。。。之后，“

2. Each letter was a seed falling on a fertile heart. (每一封信都如一颗种子撒入肥沃的心灵之土。)

第二句中现在分词等于定语从句,请问置换成 a和b，哪个更准确？谢谢。

a. Each letter was a seed that/which was falling on a fertile heart.

b. Each letter was a seed that/which fell on a fertile heart.

b正确，a错误。进行体表示动作正在进行，还没有结束，即种子还没有入土，悬浮在空中。一般过去时的动作是发生并结束的动作。该动作只要与谓语动词的时间有重叠，就可以用现在分词作定语。