As children_______, they learn from their experiences and form a picture of what the world is like.
––Would you mind _______ the music? Your grandpa is sleeping. ––Sorry. I’ll do it right away.
––_______ have you been a volunteer? ––Since three years ago.
He has been collecting coins _______ he was seven years old.
She is usually _______. Why did she get ill so suddenly?
Because of Project Hope (希望工程), _______ children have better lives.