Which sentence is written correctly?

a. ms. andrade showed us a documentary in class today because the film “focuses on a similar subject” to a book we are going to read.
b. ms. andrade showed us a documentary in class today because the film, “focuses on a similar subject” to a book we are going to read
c. ms. andrade showed us a documentary in class today because the film “focuses on a similar subject” to a book we are going to read.
d. ms. andrade showed us a documentary in class today because the film, “focuses on a similar subject” to a book we are going to read.