talk nice and polite, people listento you If you shout, this is no good,

Robert failed to complete his education____ he found it hard to focus on his studies

When were the soldiers sent to the earthquake-stricken area? — _______ the earthquake broke out

___is certain is ___prevention is more important than treatment .

Are you willing to live on Mars（火星） one day— ______________ It sounds exciting, but it still worries me.