試題詳解

46. In human, blood flows from the heart into the aorta, from which it passes into the major arteries. These branch into the small arteries (arterioles), which in turn branch into myriads of tiny capillaries. The radius of the aorta is about 1.2 cm, and the blood passing through it has a speed of about 40 cm/s. A typical capillary has a radius of about 4✖10^-4 cm, and blood flows through it at a speed of about 5x10^-4 m/s. Estimate the number of capillaries that are in the body.
(A) 1✖10⁹
(B) 3✖10⁹
(C) 5✖l0⁹
(D) 7✖10⁹
(E)9✖10⁹