47. There is a laminar flow in a tube. When both the radius and length of the tube are doubled, how many times of flow resistance is changed?
(A)
(B)
(C)
(D)
(E)
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統計: A(0), B(0), C(0), D(1), E(0) #1970701
統計: A(0), B(0), C(0), D(1), E(0) #1970701