A portion of an artery is narrowed by atherosclerotic plaque, with a radius of 2.2 mm, while the preceding part of the artery has a radius of 3.4 mm. What is the ratio of the blood's speed in the narrowed artery to that in the normal artery?
a) 1.55
b) 0.71
c) 0.51
d) 0.36
