NEW : Liang : Relationship has opportunities and challenges . The trip is Gates ' second to China since he became defense secretary . The relationship between the two sides suffered a setback last year . It is Gates ' second visit to the country since he assumed the post in December 2006 . Comment:
NEW : Liang : Relationship has opportunities and challenges . The trip is Gates ' second to China since he became defense secretary . The relationship between the two sides suffered a setback last year . Comment: