The Open Door policy was designed to A.keep the markets of China open to the United States.
B.prevent the United States from being excluded from the China markets.
C.all of the above
D.protect American access to the China trade without resorting to war.

C) All of the above.

Explanation:

According to Wikipedia, the policy was used mainly to mediate the competing interests of different colonial powers in China, including the US. Thus, the US, like other nations, wanted to access and protect its involvement in the Chinese economy.

The common options attached to this question are:
- Ireland
- France
- Arabia
- Italy

Of these four, Arabia did not contain monasteries that spread the Christian faith and preserve the knowledge of Europe. First, Arabia is not in Europe, Than also, Arabia was, and still is a predominantly Muslim area so they did not contain monasteries that spread the Christian faith in Medieval times. Furthermore, Arabs were more prone to resist western influence, so they could not have in any way preserved the knowledge of Europe in medieval times.