The answer is 'D', declarative, because it is not asking a question, it is not exclaiming anything, nor is it suggesting anything but the facts.
The earth is rather large and not exactly a point in space, the author however is comparing it to a point in space because of how vast space really is. A metaphor is basically a comparison (Not exactly true) that doesn't use the words like or as... (That's a Simile.) The earth isn't an actual dot in space. It's big, but because of how big space is, it's compared to a dot... Hope this helps... :)
To explain how wonderful to someone whos not been there
“ Didn’t you go to kindergarten”
