What is the Asthenosphere A. the middle portion of the mantle; not very dense
B. the middle portion of the mantle; extremely dense
C. the outer layer of the earth's crust
D. the inner core of the earth

What is Asthenosphere?

Ans) The Lithosphere floats on top of a semi-liquid layer. This is known as the Asthenosphere. It is the ductile inner layer of the upper mantle.

So ur accurate answer is option b.

Hope this helps you...

Jet streams are relatively narrow bands of strong wind in the upper levels of the atmosphere. the winds blow from west to east in jet streams but the flow often shifts to the north and south. jet streams follow the boundaries between hot and cold air. the earth's rotation is responsible for the jet stream as well.