Where is the top of the asthenosphere is closest to earth's surface

The top of the asthenosphere is closest to the earth's surface underneath OCEANIC CRUST. The asthenosphere is the area of the mantle beneath the lithosphere that is solid, but hotter than the rock above it. This layer can low under pressure and function as a soft , weak zone over which the lithosphere may move. 

of the two types of crust, continental and oceanic; the latter is the thinnest. oceanic crust can be as little as 5km thick while continental crust can be up to 90km thick at the mountain ranges. 

The sun's parallax would be 180 degrees, greater than which you can't get.  so a. would be your anwser 

This question has already been answered by someone else.here is a link.  hope that it .