What happens when normal human primary fibroblast cells are placed in tissue culture?

a.
they go through a fixed number of population doublings, and then they enter crisis.

b.
they go through a fixed number of population doublings, and then they enter senescence.

c.
they will divide indefinitely unless they lose their telomerase activity.

d.
they will divide indefinitely because primary cells are already immortal.

e.
they will divide indefinitely because of their telomerase activity.