As a young man, Comrade Zhou Enlai ________ the students' movements and later ________ the Communist Party of China. 

When he realized the police had seen him, the man _________ the exit as quickly as possible.

The theory       by Einstein was later to prove true, but at that time few people could accept it.

Thanks to the environment－protection policy,our living conditions have been greatly________.

People are _________the use of alternative energy sources. Because the fossil fuels _________will be used sooner or later.