(A) 50
(B) 57
(C) ** 47
(D) 55
EXPLANATIONS BELOW
Concept note-1: -The youngest person to assume the presidency was Theodore Roosevelt, who, at the age of 42, succeeded to the office after the assassination of William McKinley.
Concept note-2: -For daily wit & wisdom, sign up for the Almanac newsletter. He assumed the presidency in September 1901, after the assassination of William McKinley and shortly before his 43rd birthday. John F. Kennedy was the youngest elected president, being just 43 years of age when he took office in 1961.
Concept note-3: -In 2008, after a close primary campaign against Hillary Clinton, he was nominated by the Democratic Party for president and chose Joe Biden as his running mate. Obama was elected over Republican nominee John McCain in the presidential election and was inaugurated on January 20, 2009.