What is a likely reason an author chooses a particular theme ?

Option D.  To comment about an issue facing society

Explanation:

There are many definitions of theme. But most of them have most of the point common.

Theme may be defined as "It is deeper meaning of the story running beneath the surface meaning of the story/poetry etc. I helps reader understand the deeper meaning of the story and understand some aspects of human conditions"

Literature has always been considered mirror of life - it reflects our society either directly (Geoffrey Chaucer's Canterbury Tales)  or indirectly (Keats' "The Fall of Hyperion: A Dream). So in most cases the purpose of the theme of a literary work is to comment about an issue faced by society.

Option A is not correct because main element of theme's definition is missing in it i.e human conditions, society.

Option B is not correct also because elements of mystery and surprise are not integral parts of a literary work, while theme is an integral part.

Option C is also not correct: There's no doubt that author's life experiences shape his/her style of writing and the themes he or she chooses for his/her work. But theme is not just about author's life experiences - it is about society's life experiences.

well so many people believe its a sin to be gay or be apart of the lgbtq+ community, but i believe you should be you. don't let people tell you you cant be someone. be who you are because you will be uncomfortable your whole life. be you!