both sides accept the agreement will a lasting peace be established in this region.
A. If only
B. Only if
C. unless
D. As long as
网友回答
A. If only
(答案→)B. Only if
C. unless
D. As long as
解析：考查only的部分倒装句。Only倒装满足两个条件，only放在了句首，且强调的是状语，后面的主句使用部分倒装的形式。本题only放在了句首，强调的是条件句if both sides accept the agreement，后面的主句使用了部分倒装的形式。