What is the purpose of Squad 451 A. to be onscreen faces of the invasion
B. to be front line when they invade President Snows mansion
C. to be in charge of the aircraft invasions
D. to work closely with Beetee in district 13​

taking into account that a theme is the central topic a text treats and can be developed through a story, play, poem etc. the following are themes that can be further developed:  

my best friend jeffrey has many unusual interests. (the story could be about each of the unususal interests)

once a man gives his soul over to evil, he can never go back. (this could be a saying or a proverb)

the three sheepdogs lay around the yard all day. (it could be developed detailing how each of these sheepdogs lay around)

a priest's collar has an unusual effect upon people. (it could be developed detailing the different effect upon people)

innocence is a powerful force in a world full of corruption. (it could be developed detailing how is a world full of corruption)

king lear is a play shakespeare wrote later. (it is just a sentence and doesnt give any idea or topic to be discussed in details.

evil often wears the disguise of innocence. (this could be a saying or a proverb)

major league baseball

explanation:

jack roosevelt robinson broke the color barrier in major league baseball.as he was the first african american to play in the major leagues, jackie robinson became the target of racial abuse. jackie robinson is referring to the historic event, harlem riot.

d is the best answer for this question.