How Was It That Many Bishops Were Married Even Though

How was it that many bishops were married even though church councils demanded that the clergy be celibate?

A) Rules that applied to the general clergy did not apply to bishops.
B) Bishops were usually appointed late in life, after they had raised a family.
C) Bishops refused to obey the pope or church councils.
D) Exceptions were made for clerics who married before the ruling.