The Open Door policy was a statement of principles initiated by the United States in 1899 and 1900. It called for protection of equal privileges for all countries trading with China and for the support of Chinese territorial and administrative integrity.
An open door policy is a communication policy in which a manager, CEO, MD, president or supervisor leaves their office door "open" in order to encourage openness and transparency with the employees of that company.
The United States broke diplomatic relations with Germany, because Germany declared unrestricted submarine warfare against all ships. The correct answer is C.
