What is the fastest way to unlock cars in gta online?

The source supplied only describes Grand Theft Auto IV, a 2008 action‑adventure game set in Liberty City. It covers the single‑player storyline, setting, and gameplay mechanics such as third‑person perspective and vehicle use. No details are given about Grand Theft Auto Online, car unlock mechanics, or any fastest methods for acquiring vehicles. Therefore, based solely on the verified information, the question about unlocking cars in GTA Online cannot be answered.