 Criticism of Du Fu 's works has focused on his strong sense of history , his moral engagement , and his technical excellence . 
 Criticism of Du Fu <a href='null_genetive' title='1'><mark>'s</mark></a>works <a href='been_done' title='2'><mark>has</mark></a> focused on his strong sense of history , his moral engagement , and his technical excellence . 
Criticism of Du Fu  works done focused on his strong sense of history , his moral engagement , and his technical excellence .