消化性溃疡最常见的并发症为______________。
参考答案：上消化道出血
补体活性片段中的趋化因子是（）
A.C2a
B.C5a
C.C4a
D.C4b
E.C3b
A revocable Letter of Credit is one that can not be cancelled by the issuing bank without the seller’s agreement.
