Final answer:
The fluid mosaic model of membrane structure describes the plasma membrane as a mosaic of components that can move fluidly within the plane of the membrane.
Step-by-step explanation:
The fluid mosaic model of membrane structure describes the plasma membrane as a mosaic of components that can move fluidly within the plane of the membrane. This means that proteins can easily move laterally through membranes, which is the correct answer to your question (b). Lipids, on the other hand, can move laterally in the membrane, but they do not flip from one leaflet to another as easily as they can move laterally. So, option (d) is not true. Membranes behave more like a fluid than a solid, which refutes option (a). And proteins can move across membranes, but not easily, so option (c) is not true either.