Diaoyu Island issue, unless properly, will directly affect smooth development of relationships between China and Japan.
A. handling
B. having handled
C. to handle
D. Handled
网友回答
A. handling
B. having handled
C. to handle
(答案→)D. Handled
解析：句意:钓鱼岛问题，如果不处理不得当，将直接影响中日关系的顺利发展。这里unless后是省略句，完整的是unless it ishandledproperly，这里it is省略了，故选D。