Determine Ms. Arnout's filing status in each of the following independent cases.

a. Ms. Arnout and Mr. Eckes have been living together since 2016. They were married on December 13, 2018.

b. Ms. Arnout married Mr. Pritchett in 2011. They were divorced on November 8, 2018, and have no dependent children.

c. Ms. Arnout married Mr. Pritchett in 2011. They separated in 2017 and have not lived together since, but they have not divorced.

d. Ms. Arnout divorced Mr. Pritchett in 2018. She maintains a home for herself and her dependent grandmother.