The plan ________encourage the employees to improve their work turned out to be a success.
The teacher ___________his students to work hard.
After the age of 50 people often _____________ their individual ambitions.
He is a key ____________ in the murder so we must protect him from all kinds of danger.
Russia is _________ on the north of China.
Lately some scientists are experimenting ___________ white mice to ____________ this kind of medicine.