9.  Which of the following helps differentiate portal systems from other circulatory routes? B
the absence of capillary beds
Incorrect.
two sets of capillary beds   
Correct!
three sets of capillary beds
Incorrect.
unusually large arteries and veins
Incorrect.
the absence of arterioles and venules
Incorrect.

[#FRAME:"TRM3S2D"]
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