How can I import dropdown options?
There are several extensions designed to do exactly this.

First is the aptly-named Option Values Importer.  It hasn't been updated recently, and it only does the one thing - but it may be simpler to use as a consequence.

There's the configitems extension.  This one has a bit more setup, but is great if you have to add/remove values on a regular basis.

Finally, there's the CSV API GUI extension.  This is an alternative to the "API Explorer" approach Pete suggests, that lets you import in bulk from a CSV file.  This works with all modern versions of CiviCRM and is probably the best bet if you don't want to mess with putting files into your web server's file system.