Final answer:
The primary way that the search for extraterrestrial intelligence (SETI) is carried out at present is by using radio telescopes to search for signals from extraterrestrial civilizations.
Step-by-step explanation:
The primary way that the search for extraterrestrial intelligence (SETI) is carried out at present is C) by using radio telescopes to search for signals from extraterrestrial civilizations. Scientists believe that radio waves are the best way to communicate with intelligent civilizations in outer space. Radio telescopes, such as the Allen Telescope in Northern California and the Arecibo radio dish in Puerto Rico, are used to scan different frequencies and search for potential signals from advanced civilizations.