When the reactions are not growth limiting,the growth curve is . . . . . . .

Read the following statements and determine how many of them are correct:
$(1)$ Population is the total number of individuals of a species in a given area at a given time.
$(2)$ Developed countries show a low birth rate.
$(3)$ An equal proportion of reproductive and post-reproductive age individuals indicates a stable population.
$(4)$ In the presence of limited resources,the growth curve is sigmoid ($S$-shaped).

The carrying capacity of a population is determined by its

An asymptote in a logistic growth curve is obtained when:

In the given figure,what do $a$ and $b$ represent respectively?

Population growth is reduced by environmental resistance. This phase is known as: