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