单项选择题
In the umbilical cord, there are ( ).
A、2 umbilical arteries and 1 umbilical vein
B、1 umbilical artery and 1 umbilical vein
C、3 umbilical arteries and 1 umbilical vein
D、1 umbilical artery and 2 umbilical veins
E、2 umbilical arteries and 2 umbilical veins
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