Warm areas in the asthenosphere are thought to be

a) expanding and rising.
b) expanding and sinking.
c) contracting and rising.
d) contracting and sinking.

a) expanding and rising.

Explanation:

Warm areas of the asthenosphere are generally believed to be expanding and rising. The cold areas are contracting and sinking.

We can picture the asthenosphere as pot of wax. As the pot is heated, the wax at the bottom of the pot rises and expands. The wax on top begins to fall to the bottom of the pot. A convective cell is eventually set up where cold wax sinks and hot wax rises.

This is the same mechanism at work in the asthenosphere. Colder part of the asthenosphere are denser and they sink like the cold wax top. The lighter part of the asthenosphere rises and upwells.