13. Membranes with unsaturated fatty acids in their components are more flexible and fluid because:
(A) Unsaturated fatty acids pack closely together to form ordered arrays.
(B) Unsaturated fatty acids bend at the double bond preventing close packing.
(C) Saturated fatty acids have a "kink" that produces more fluid aggregates.
(D) Unsaturated fatty acids have cis double bonds that prevent formation of the "kink."
(E) All of the above are correct.