Determine Ms. A's filing status in each of the following independent cases:
a. Ms. A and Mr. Z have been living together since 2015. They were married on December 13, 2017.
b. Ms. A married Mr. P in 2010. They were divorced on November 8, 2017, and have no dependent children.
c. Ms. A married Mr. P in 2010. They separated in 2016 and have not lived together since, but they have not divorced.
d. Ms. A divorced Mr. P in 2017. She maintains a home for herself and her dependent grandmother.