Answer: A. Of German aggressions against British ships and the Zimmermann Telegram
Explanation: One of the direct reasons for the entry of the United States into the First World War was the sinking of the passenger ship Lusitania, also with American travelers on it. Prior to this, America was outraged with the German U-boats, and its unrestricted sinking of allied ships in the Atlantic.
Zimmermann telegram was the offer by Germany in January 1917, sent to Mexico to be a German ally, in the event that America entered the WWI. In return, Mexico would recover Texas, New Mexico, and Arizona.