The correct answer is D. when in equilibrium, fluids can sustain shear forces.
A fluid is a substance that can flow and take the shape of its container. Fluids are made up of tiny particles that are constantly moving. These particles can slide past each other, which is why fluids can flow.
When a fluid is in equilibrium, the particles are not moving relative to each other. This means that the fluid cannot sustain shear forces. Shear forces are forces that try to cause the particles in a fluid to slide past each other. If a fluid is in equilibrium, the particles cannot slide past each other, so the fluid cannot sustain shear forces.
Options A, B, and C are all correct statements about fluids. A fluid is capable of flowing, and it conforms to the shape of its container. When a fluid is in equilibrium, it cannot sustain tangential forces.