The particles of a medium will settle the rest position after a mechanical wave passes
a. at
b. behind
c. in front of

After the mechanical waves passes by, the particles of the medium will settle right back at their rest position (A).  

It doesn't matter whether the wave was a longitudinal or a transverse one.

frequency or wavelenth of em radiation in a vacuum

d. platinum would have the greatest temperature increase because it has the lowest specific heat.