At the end of the novel, scout mentions killing a mockingbird. this can most be connected to theme of
a the need for empathy and understanding
b the importance of social justice
c the ways in which a community comes together
d moral courage

The answer to your question would be option B, the importance of social justice.

Explanation:

The topic of social justice can be found throughout the novel To Kill a Mockingbird. For example the author of the book describes several social justice issues that affect a number of people in the novel, such as racism.

Through the book, certain characters such as Scout, confront the difficult truths about racism, and at the end of a novel, when she mentions killing a mockingbird, it can be inferred that she refers to the theme of social justice as, through her journey, Scout has learnt that while courts are a source of justice, there are also other ways of achieving justice outside of it.

the best sentence that shows the best placement for the modifier "on the ice" is the one which contains it in the end of the sentence or in its beggining followed by a comma, that indicates it works as adverbial, dislocated in the sentence.

the girl promptly slid on her rollers on the ice.

on the ice, the girl promptly slid on her rollers.