In the models that describe population growth, r stands for
a) carrying capacity
b) population density
c) a time interval
d) per capita population growth rate
e) total number of individuals in the population

d) per capita population growth rate

Explanation:

Per capita growth rate of a population is symbolized as "r" in population growth models. Here, "r" is the rate of change of a population on a per capita basis. The change in the population includes both an increase and a decrease in its size.  The per capita growth rate is calculated by subtracting the birth rate of the population from its death rate. Therefore, r= b-d. Here, "b" is the birth rate of the population and "d" is the death rate.

ocean expansion, global warming is melting icebergs and causing water levels to rise.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.