Which of the following statements correctly describes a difference between plant cells and animal cells?
a. plant cells have an envelope surrounding the nucleus. animal cells do not.
b. animal cells contain mitochondria. plant cells do not.
c. animal cells contain chloroplasts. plant cells do not.
d. plant cells are surrounded by a cell wall. animal cells are not.

D) Plant cells are surrounded by a cell wall. Animal cells are not.

Explanation:

Plant cell needs cell wall whereas animal cell do not because the plants need rigid structure so that they can grow up and out, thus animal cells do not have cell walls. So therefore, D is the correct answer.

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.