The primary reason the united states advocated the open door policy in 1899 was to
(a) consolidate good relations between the united states and european countries holding leases in china
(b) encourage asian nations to protect chinese interests
(c) expand the effort of european nations to westernize china
(d) protect united states missionaries in china
(e) protect united states trading opportunities in china

Open Door Policy (1899/1900) is declaration of principles introduced by the United States (1899, 1900) for the defense of equal freedoms amid nation’s transaction with China and in provision of Chinese regional and directorial honesty. So the answer is E.

The correct answer is (E) protect United States trading opportunities in China

China was a huge market and everyone wanted to be in on it and to trade with them. This created the opportunity with countries to sign deals with China which would make them exclusive when it came to Chinese trading. The US wanted to prevent this by initiating the open doors policy in order to make China fair ground for all countries, which naturally meant that they could maintain their trading with China.