Our teacher is always busy preparing lessons until 11 o’clock at night, _____we students have gone to sleep.

Shall we go skating or stay at home?—Whichdo yourself?

use, ______walls are red, is where mygrandfather used to live ten years ago

Bill doesn’t do well in his English. So his father asked a teacher ____ him ____ it.

The book was written in 1946, the education system has witnessed great charges.