With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: After German submarines conducted total and unconditional warfare against American shipping in British waters, the USA formally declared war on Germany in April of 1917. With the U.S. mobilizing for war, President Woodrow Wilson appointed Hoover to head the U.S. Food Administration, which was charged with ensuring the nation's food needs during the war. Hoover had hoped to join the administration in some capacity since at least 1916, and he obtained the position after lobbying several members of Congress and Wilson's confidant, Edward M. House. Earning the appellation of "food czar", Hoover recruited a volunteer force of hundreds of thousands of women and deployed propaganda in movie theaters, schools, and churches. He carefully selected men to assist in the agency leadership—Alonzo Taylor (technical abilities), Robert Taft (political associations), Gifford Pinchot (agricultural influence), and Julius Barnes (business acumen).
text_B: Given what can be learned from this passage, would it be reasonable to assume that uniformed American sailors had been fired up, and possibly even killed, by German U-Boats prior to April of 1917 without this technically being an act of war against the US?
NO.