The definition of an incompressible fluid is
Select one:
a. A fluid with a constant density at all pressures
b. A fluid with no viscosity
c. A fluid with a constant pressure
d. A fluid with viscosity
well, if it's incompressible, then its volume doesn't change under pressure, right?
SO, since the mass also doesn't change, that must mean that the answer is
(A), since density = mass/volume, both of which are constant.