The purpose of the open door policy is to collaborate with other nations to maintain a common price level for free trade in china
. Option B is correct.
Open Door policy refers to an set of principles started by the United States in 1899 and 1900 in order to protect equal privileges among countries trading with China and in support of Chinese territorial and administrative integrity.
The principle that all countries should have equal access to any of the ports open to trade in China had been outlined in the Anglo-Chinese treaties of Nanjing and Wangxia.
