Fall by the wayside means to fail to continue or be abandoned. The correct answer is this meaning because the expression is used figuratively, not only by its literal words.

Examples:

• Many early plans fell by the wayside.
• In an HSC essay, Fall by the wayside can express this meaning: to fail to continue or be abandoned.
• When this expression appears in a passage, connect Fall by the wayside with the idea of to fail to continue or be abandoned.