Below are two variations of the same sentence.
I would like to know if a comma should follow the initial clause in both setences.
I'm quite certain that (A) should use a comma, but i'm not so sure about (B). i suspect no comma is needed here, although i don't know why
(A) "Reading the book [,] I found it all came together"
(B) "When I read the book [, ] ? it all came together"