With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: The protagonist of the game, Colonel John R. ("Rusty") Blade, is the commander of one of the largest security forces in the city of Freeport, HardCorps. Prior to the beginning of the game, Blade is working to rid the streets of a potent new recreational drug named U4, which is rapidly gaining popularity in Freeport and is rumoured to be able to cause genetic mutations to its users. Yet the source of the drug is still a mystery, and its effects not entirely studied. As the game begins, the player is placed into the shoes of John Blade as he responds to a full-scale bank heist and hostage situation perpetrated by a well-known Freeport criminal boss, Antonio Mancini. But as the player progresses and pursues the criminal behind the heist, further questions are raised: Who is really behind the heist? And is this linked to the reported appearances of mutants in the city?
text_B: Would doctors be able to identify any of the symptoms of U4 use in a patient?
YES.