The book was written in 1946, _______ the education system has witnessed great changes.
A．since then B．when C．since when D．during which
He ______ be sitting at the gate, waiting for his lost son.
A．used to B．was used to C．could D．was accustomed
It is often recommended that children _______ chances to get close to nature.
A．must be offered B．should offer C．be offered D．are offered
If you _____ the bottle and cigarettes, you we’ll be much healthier.
A．take off B．keep off C．get off D．set off
— Will 1000 dollars ______ the bill?
— Of course, more than sufficient.
A．cover B．pay C．contain D．include
—You must do as I told you.
— ______ I don’t?
A．What about B．How about C．Only if D．What if
