In John 1:1c, should the Greek word θεὸς be translated into English as “a god” or “God”?

The New World Translation, the official Bible version of the Watchtower/Jehovah’s Witnesses, translates John 1:1 into English as follows: 1 In the beginning was the Word, and the Word was with God, and the Word was a god. NWT, 2013 T…