---My son isn’t good at math. Could you please give him ?--- Sure.
The story _______ about fifty years ago.
He arrived____ London ____ a cold winter night.
When I walked past her room, I heard her _______ an English song.
Keep the machine _______, and you will know how it works.
—What was Tom doing _______ it was raining?—He was doing his homework in the bedroom.