On average how large are convection cells? 10 degrees in latitude, 30 degrees in latitude, or 50 degrees in latitude?

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

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

Which is the most reasonable capacity of a water pitcher. m a 2 ml b 20 ml c 2 l d 20 l