--Where is Xiao Wang? --I don't know. He__________ be in the library.
I __________ the names of plants.
The bus was due to __________ at 5 p. m.,but it arrived one hour late due to __________ by the heavy fog.
The professor devoted all his life __________ the treatment of AIDS.
He was __________ down for several days after he heard the bad news.
They all looked down upon him. He was __________ a singer.