How did studies of the crab nebula pin down the explanation of pulsars?

The primary agent of contact metamorphism is

Alow pressure system is formed when an air mass cools over a cool surface and sinks. true or false

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.