Which of the following could be said about ecological footprints? a. ecological footprints can't be used to determine carrying capacity. b. the average ecological footprints for various countries are nearly identical. c. ecological footprints don't take into account resources needed to absorb and manage wastes. d. exact ecological footprints are often difficult to calculate, but estimates can be useful in comparing populations.

D. Exact ecological footprints are often difficult to calculate, but estimates can be useful in comparing populations.

The ecological footprint refers to the estimation of the productive ecological area used by the human population to meet it's requirement of natural resources like fruits, vegetable, fish, wood, fossil fuel extraction, space used for construction and for other purposes. It is also concerned about the amount of resources used. The exact ecological footprints are often difficult to calculate because of large area being under use of human population and use of resources in the routinely way. The data collection is related with inaccuracies and requires huge financial demand. A rough estimate can be prepared which distinguishes the use of land and other resources at global, country and state level.

the second type of galaxy is called a barred spiral, which has a thing called a bar straddling the nucleus

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.