With the word "PM2.5"______ heard and seen in our life, people become more and more concerned about air pollution.
The boy seems __________ a lot of books, for he knows so much.
He is so addicted to smoking that __________ seems to be no chance of talking him into quitting.
The Roman Empire __________ for several centuries.
-How long has the United Nations __________?-__________1945.
It seems __________ the poor guy is going to die of __________.