Answer the following question: WASHINGTON----Chinese Vice-President Xi Jinping arrived at Andrews Air Force Base in Washington,February 13,2012.Vice-President Xi Jinping said he would explore important problems in an active and practical manner with his America hosts on Monday during his five-day official trip here after arriving at Andrews Air Force Base in the afternoon. In a written statement given upon his arrival,Xi said as the international situation experiences complex and complete changes,China and the United States have more extensive common interests and shoulder more important common responsibilities on the present world stage. The purpose of the current visit is to "carry out the important _ reached by President Hu with President Obama during his visit to the United States in January last year and to advance the building of the China--US cooperative partnership based on mutual respect and mutual benefit",said Xi. According to Xi,bilateral relations have moved forward in spite of some twists and turns during the past several decades. "This has brought enormous benefits to our two countries and two peoples,and has had a positive, far-reaching impact on peace,stability and the prosperity of the Asia-Pacific region and the world at large". Xi said that"whether we can seize opportunities,tackle challenges and build a cooperative partnership at the new historical starting point matters to the future of our two countries and the world as a whole." Xi said he looks forward to engaging in extensive dialogue and exchanges with Americans from various sectors to enhance cooperation and strengthen friendship. Xi is scheduled to meet US senior government officials,including Henry Kissinger,Brent Scowcroft,Zbigniew Brzezinski,Madeleine Albright and Henry Paulson this evening to listen to their advice on China-US ties. Meetings between Xi and US Vice-President Biden and President Obama are scheduled on Tuesday. According to tile passage,bilateral relations between China and US have experienced _ . A) enormous dialogues B) extensive exchanges C) rnany challenges D) various hardships
Answer:
D