21. 下列何者是甲狀頸動脈幹(thyrocervical trunk)的分支? (A)甲狀腺下動脈(inferior thyroid artery) (B)甲狀腺上動脈(superior thyroid artery) (C)椎動脈(vertebral artery) (D)肩胛下動脈(subscapular artery)