This book *is/was* written *in English by Sam/by Sam in English*.
a. This book was written in English by Sam.
b. This book was written by Sam in English.
Are the two sentences above correct? Are there any differences between them? Which is more common? And I know that Sam did write the book in the "past", so we should use the past tense here, but if we view it as a "fact", can I say "is" instead of "was"? Thanks!