along shorelines
First, look at the definitions involved.
hydrosphere - All the water on earth's surface such as lakes and seas.
lithosphere - The rigid outer part of earth's crust.
Now look at the available choices:
on mountaintops
* Bodies of water aren't too common up on mountain tops. Not a good choice.
inside glaciers
* Inside glaciers? Not touching earth, but lots of ice instead. Also not a good choice.
at volcanoes
* Not a lot of water here either. Bad choice.
along shorelines
* Sounds good. The boundary between water and earth. This is the right answer.
