Since bicycles became so popular, there has been an increase in the number of accidents.

increase 是动词 increase 的名词形式，表示"增加、增长"的意思。这里指事故数量上升的现象。 increase 由前缀 in-（表示"向内、进入"）和词根 crease（来自拉丁语 crescere，意为"生长"）组成，字面意思是"向内生长"，引申为"增加"。