During allopatric speciation
a: a geographic separation occurs between subpopulations
b: reproduction between all subpopulations is impossible
c: wide phenotype differences appear between subpopulations
d: gene flow continues between subpopulations
e: subpopulations are still able to interbreed

A. a geographic separation occurs between subpopulations

Explanation:

Allopatric speciation, which can also be called geographic speciation, is a type of speciation that involves the isolation of biological populations of the same species. This isolation is caused by geographical changes which include, formation of islands, mountains, and bodies of water. Social changes, brought about by human activities such as urbanization and agriculture, also aids Allopatric speciation.

The isolation of subpopulations from each other will lead to the gene flow being interfered or hindered.

where is the diagram?

if you insert the diagram ill be able to you

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.