【答案解析】This rule reveals two points: first, it shows one possible allomorph of the morpheme {D}, and this allomorph has the phone [-id] as its element; second, it shows the according phonetic environment in which that allomorph can occur, that is, it will be pronounced as [-id] when it appears after the phone [t]. In this rule, the arrow means the realization, and the bar indicates the environment of the target element.