The correct answer is C.
Wilson tried his best to maintain a policy of neutrality at the beginning of World War I. However, after the Lusitania was sunk and over 100 innocent Americans were killed, he knew action must be taken.
In response to the sinking of this ship, Wilson wrote several letters to the German government. In these letters, Wilson demanded that Germany stop their use of unrestricted submarine warfare. Wilson wrote this in hopes that Germany would not sink anymore ships with US citizens on it. Germany complied for a short period of time, but resumed these actions less than a year later. This is one of several different factors as to why the US entered World War I.