 sentence1: {"placeholder":"text_a"} sentence2: {"placeholder":"text_b"} {"mask"}
 {"placeholder":"text_a"} {"placeholder":"text_b"} {"mask"}
 sentence1: {"placeholder":"text_a"} sentence2: {"placeholder":"text_b"} The answer was {"mask"}
 sentence1: {"placeholder":"text_a"} sentence2: {"placeholder":"text_b"} answer: {"mask"}
 