The Defense of Shado-Pan Fallback[1] has two missing quest prerequisite for it to unlock. The missing prerequisite quests is All of the Arrows[2] and Hit Medicine[3]

[1] https://www.wowhead.com/quest=30665/the-defense-of-shado-pan-fallback
[2] https://www.wowhead.com/quest=30459/all-of-the-arrows
[3] https://www.wowhead.com/quest=30460/hit-medicine