The Decisive Point in the Opium War Was

The decisive point in the Opium War was

A) the British threat to the Grand Canal.
B) the arrival of an American fleet to aid the British.
C) a surprise British attack on the Chinese fleet at Port Arthur.
D) the overwhelming numbers of Chinese forces as they,although outgunned,overran British outposts.
E) a sudden reversal by China's erstwhile ally,the Japanese.