Answer
D.
Work Step by Step
Membrane proteins add function to the membrane, which gives the membrane its role/identity in the cell, making D. true. A. does not affect function, and can vary widely over time in the same membrane, and so is wrong, and B. does not determine function, though particular functions are often placed by the cell in particular locations. C. also does not have much bearing on membrane function--it is proteins which make the difference.
