Break ranks means to stop supporting a group and act independently. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• Several members decided to break ranks and oppose the policy.
• In an HSC essay, Break ranks can express this meaning: to stop supporting a group and act independently.
• When this expression appears in a passage, connect Break ranks with the idea of to stop supporting a group and act independently.