 A {"mask"} news : {"placeholder": "text_a"} {"placeholder": "text_b"}
 {"placeholder": "text_a"} {"placeholder": "text_b"} This topic is about {"mask"} .
 [ Category : {"mask"} ] {"placeholder": "text_a"} {"placeholder": "text_b"}
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 {"placeholder": "text_a"} {"placeholder": "text_b"} {"special": "<sep>"} This topic is about {"mask"} .
