21. 下列何者穿行於脾腎韌帶(splenorenal ligament)內？ (A)脾動脈(splenic artery) (B)左胃動脈(left gastric artery) (C)左胃網膜動脈(left gastro-omental artery) (D)胃十二指腸動脈(gastroduodenal artery)