The correct answer is A) He was named acting president.
Vladimir Putin first became president of Russia when he was named acting president.
On December 31, 1999, Russian President Boris Yeltsin resigned and chose Vladimir Putin as his successor. Russian government organized elections three months later after Yeltsin's resignation. So in the Presidential elections of March 2000, Vladimir Putin was declared the winner. He easily defeated his rival Gennady Zyuganov, who at that time was the leader of the strong Communist Party.
Since that election, Putin has been reelected many times and he is the absolute leader of Russia and one of the most powerful leaders of the world.