What Is the Difference Between the 'Open Style' and the 'Mixed

Multiple Choice

What is the difference between the 'open style' and the 'mixed style' in punctuation for business letters?

A) Whether or not there is a comma after 'Yours sincerely'
B) Whether or not there is a comma after the salutation and the complimentary close
C) Whether or not there is a comma after 'Yours faithfully'
D) Whether or not there are commas throughout the body of the letter