Index fossils found in rocks can be used to help determine the rock's age, because index fossils are fossils of species that .
a changed their diets
b hid in marine sediments
c migrated to different environments
d quickly became extinct

These factors threaten north americas ecosystems

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.

The plants growing on scotlands highland moors are a)mixed forestb)grasses and low shrubsc)evergreen treesd)palm trees and ferns