Look,the boy is falling off the bike. falling off 是固定搭配. Noun 1.a noticeable deterioration in performance or quality; "the team went into a slump"; "a gradual slack in output"; "a drop-off in attendance"; "a falloff in quality" (synonym) slump,slack,drop-off,falloff (hypernym) deterioration,decline in quality,declension,worsening
