vi.中间呈V形弯； 变形： 过去式：jack-knifed现在分词：jack-knifing第三人称单数：jack-knifes 英英释义： jack-knifen.a large knife with one or more folding blades同义词：clasp knifejackknifea dive in which the diver bends to touch the ankles before straightening out同义词：jackknifev.dive into t