The answer to the item above is letter "C. surface". Surface waves are mechanical waves that propagate in the interface of differing media. These waves very usually have larger altitudes and longer wavelengths than the body waves.
For many years scientists have studied our own solar system. But until the last few years, we knew of no other solar systems. This may seem surprising, as the Sun is one of about 200 billion stars (or perhaps more) just in the Milky Way galaxy alone.
