Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. Ex-Adviser, Diplomat to Testify in Trump Impeachment Inquiry VOA News Two additional advisers will testify Thursday as the U.S. House of Representatives holds a marathon week of public hearings on the impeachment inquiry into President Donald Trump. Former White House adviser Fiona Hill and career foreign service officer David Holmes are to testify Thursday. On Tuesday Jennifer Williams, an aide to Vice President Mike Pence, and Lt. Col. Alexander Vindman, the National Security Council's top Ukraine expert, former U.S. Special Envoy to Ukraine Kurt Volker and former NSC official Tim Morrison testified. On Wednesday, the most high-profile witness to appear, U.S. Ambassador to the E.U. Gordon Sondland, testified for nearly seven hours. He was followed by career Pentagon official Laura Cooper and Undersecretary of State David Hale Wednesday afternoon. All nine have testified previously in closed-door hearings about Trump's efforts to pressure Ukraine to investigate his political rival, former Vice President Joe Biden and his son, Hunter, who had served as a board member of a Ukraine natural gas company, and probe a discredited conspiracy theory regarding the 2016 president election. Three of the nine listened in on the July 25 phone conversation between Trump and Ukraine's president. Democrats hope the hearings will sway public opinion in favor of impeachment. Republicans have used them to discredit the impeachment proceedings and poke holes in the witnesses' testimony. Here is what you need to know about the witnesses Thursday and their role in the Ukraine affair. .