17."Density-dependent inhibition" is explained by which of the following? 
(A)As cells become more numerous, the amount of required growth factors and nutrients per cell becomes insufficient to； allow for cell growth.
(B)As cells become more numerous, they begin to squeeze against each other, restricting their size and ability to produce control factors.
(C)As cells become more numerous, the level of waste products increases, eventually slowing down metabolism.
(D)As cells become more numerous, more and more of them enter the S phase of the cell cycle.
(E)As cells become more numerous, they begin to squeeze against each other, restricting their size and ability to produce control factors.