Which of the following formulas can be used to measure exponential growth?

If a population growing exponentially doubles in size in $3$ years,what is the intrinsic rate of increase $(r)$ of the population?

If in a population of size $N$,the birth rates are represented as $b$ and death rates as $d$,then the increase or decrease in $N$ during a unit time period $t$ will be:

If $N$ is the population density at time $t$,then its density at time $t+1$ can be calculated as . . . . . . .

Any species growing $A$ under unlimited resource conditions can reach enormous population densities in a short time. Darwin showed how even $B$ growing animal like elephant could reach enormous numbers in absence of check and that characteristics of organism is called $C$. Choose the correct option for $A, B$ or $C$ respectively.

$I.$ Populations evolve to maximize their reproductive fitness,also called Darwinian reproductive fitness (higher $r$ value),in the habitat in which they live.
$II.$ The population growth rate $r$ is inversely related to generation time.
$III.$ The housefly,which has a short life span and produces a large number of eggs,could be considered as a '$K$' selected species.
$IV.$ Under a particular set of selection pressures,organisms evolve towards the most efficient reproductive strategies.
$V.$ Life history traits of organisms have evolved in relation to the constraints imposed by biotic and abiotic factors in their habitat.
Select the combination of correct statements.