Soon after the discovery of nerve growth factor (ngf), researchers injected newborn mice with rabbit antiserum (i. e. rabbit serum that contains antibodies) that recognize and neutralize mouse ngf. they observed massive nerve cell death compared to appropriate control injections (e. g. injection of rabbit antiserum that doesn't recognize ngf), up to 99% of the neurons in some parts of the developing peripheral nervous system died after about a week of daily injections. which of the following conclusions is supported by these results?

a. ngf signaling sensitizes developing nerve cells to apoptotic signals.
b. developing neurons undergo apoptosis in the presence of rabbit proteins.
c. developing neurons require ngf for apoptosis.
d. developing neurons undergo cell death in the absence of ngf.
e. ngf signaling is sufficient for survival of the developing neurons.