It can be confusing. Some Jews pronounce the word Shabbat while others say Shabbos, some say Bat Mitzvah while others say Bas Mitzvah, some say Matzah while other says Matzo. Which pronunciation is correct?

Over the years different Jewish communities have varied in how they pronounce Hebrew. How did these differences come about? How many different pronunciations of Hebrew are there? Who is closest to the original?