Question: Khizir Khan spoke at the convention in Philadelphia that nominated which person for Democratic presidential candidate?

<P0-S0> In United States presidential elections, an unpledged elector is a person nominated to stand as an elector but who has not pledged to support any particular presidential or vice presidential candidate, and is free to vote for any candidate when elected a member of the Electoral College. <P0-S1>  Presidential elections are indirect, with voters in each state choosing electors on Election Day in November, and these electors choosing the President of the United States and Vice President of the United States in December. <P0-S2>  Electors today are elected in every state by popular vote, and in practice have since the 19th century almost always agreed in advance to vote for a particular candidate — that is, they are said to have been "pledged" to that candidate. <P0-S3>  In the 20th century, however, several elections were contested by unpledged electors, who made no pledge to any candidate before the election. <P0-S4>  These anomalies largely arose over fissures within the Democratic Party over the issues of civil rights and segregation. <P0-S5>  No serious general election campaign has been mounted to elect unpledged electors in any state since 1964. <SEP> <P1-S0> The 2016 Democratic National Convention was a presidential nominating convention, held at the Wells Fargo Center in Philadelphia, Pennsylvania, from July 25 through to July 28, 2016. <P1-S1>  The convention gathered delegates of the Democratic Party, the majority of them elected through a preceding series of primaries and caucuses, to nominate a candidate for president and vice president in the 2016 United States presidential election. <P1-S2>  Former U.S. Secretary of State, Hillary Clinton, was chosen as the party's nominee for president by a 59.67% majority of delegates present at the convention roll call, defeating primary rival Senator Bernie Sanders, who received 39.16% of votes from delegates, and becoming the first female candidate to be formally nominated for presidential by a major political party in the United States. <P1-S3>  Her running mate, Senator Tim Kaine from Virginia, was confirmed by delegates as the party's nominee for vice president by acclamation. <SEP> <P2-S0> The 2016 Libertarian Party presidential primaries and caucuses allowed electors to indicate non-binding preferences for the Libertarian Party's presidential candidate. <P2-S1>  These differed from the Republican or Democratic presidential primaries and caucuses in that they did not appoint delegates to represent a candidate at the party's convention to select the party's nominee for the United States presidential election. <P2-S2>  The party's nominee for the 2016 presidential election was chosen directly by registered delegates at the 2016 Libertarian National Convention, which ran from May 26 to 30, 2016. <P2-S3>  The delegates nominated former New Mexico Governor Gary Johnson and former Massachusetts Governor Bill Weld. <SEP> <P3-S0> Khizr Muazzam Khan (born 1950) and Ghazala Khan (born 1951) are the Pakistani American parents of United States Army Captain Humayun Khan, who was killed in 2004 during the Iraq War. <P3-S1>  The couple received international attention following a speech at the 2016 Democratic National Convention that criticized Republican presidential candidate Donald Trump.