Answer
B.
Work Step by Step
A. is not true since the contents of the bilayer can affect how quickly a nonpolar molecule crosses a membrane but not whether it does so, and B. is true because concentration gradients drive diffusion--whether the molecule will cross depends on the appropriate concentration gradient being present. C. is not true since a nonpolar molecule can cross the membrane without the help of proteins. Since A. and C. are wrong, D. is also wrong.
