An ideal incompressible fluid flows through a 4.0-cm diameter pipe at 1.0 m/s. There is a 2.0 cm diameter constriction in the line. What is the speed of the fluid in this constriction?
a) 0.25 m/s
b) 0.50 m/s
c) 2.0 m/s
d) 4.0 m/s