单项选择题
A.2~3cm B.4~6cm C.3~4cm D.1~2cm E.6~8cm
A.直肠下静脉 B.卵巢静脉 C.肾上腺静脉 D.髂内静脉 E.肠系膜下静脉
A.10% B.20% C.50% D.60% E.60%以上