Answer
See explanation
Work Step by Step
Fluidity refers to movement within a single leaflet, which is rapid.
Asymmetry refers to differences between the two leaflets, which are maintained over time because flip-flop between leaflets is energetically unfavorable and requires enzymes.
So the membrane can be fluid in-plane (lipids moving side-to-side) while still being asymmetric across leaflets.
Because fluidity of the bilayer is based on one plane, lipid molecules diffuse laterally in a monolayer but do not flip between these specific monolayers. Thus, specific lipid molecules inserted into one monolayer remain in it unless they are actively transferred by a flippase enzyme
