scientists have determined the composition of the lithosphere and asthenosphere but have struggled to discover much about the lower mantle (mesosphere). what are the compositions of the upper two parts of the mantle? why is it difficult for scientists to learn about the mesosphere? How could they try to gather more information about it?

Explanation:

The lithosphere is composed of the crust and a  portion of the upper mantle. the athenosphere is partially molten upper mantle material that behaves plasticly & can flow.

It is harder to work on the lower layers because its gets extremely hot & sometimes it can get so hot that it melts tools used  to research these layers.  

the answer is d. 4

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