Which of the following is probably the main factor responsible for the phenomenon of density-dependent inhibition?

a. a local accumulation of growth-inhibiting factors
b. a local deficiency of nutrients
c. cells' inate "sense" of knowing when the organ of which they are apart has no need for additional cells
d. a shortage of growthfactors
e. none of the choices are correct

2 answers

http://en.wikipedia.org/wiki/Density-dependent_inhibition
I believe that it is none of the choices. I have read the chapter, and I am not 100% sure, but a,b,c, or d just don't seem right.