Which of the following describes how scientists separate the chemical layers of the Earth? Group of answer choices

A Based on how the layers interact with each other

B Based on the atoms and molecules in each layer

C Based on the color of each layer

D Based on the size of each layer

At which point on the diagram do convection currents occur to drive plate movement?

Which of the following statements best characterizes changes to agriculture in the united states since 1900? a. increased mechanization has reduced the need for labor.b. increased mechanization has increased the need for water, thereby increasing the need for labor.increased mechanization has increased the use of land, thereby increasing the need for labor.d. increased mechanization has increased food production, thereby increasing the need for labor. select the best answer from the choices provided.

Given: circle a externally tangent to circle b. how many possible common tangents to circles a and b can exist? 2 3 4