21. —I don't think I can walk any further!
—________. Let's stop here for a rest.
A．Neither am I B．Nor can I
C．I don't think so D．I think so
22. The machine has been used much too long. ________ it doesn't work well sometimes.
A．It's no wonder that B．There is no doubt if
C．It's unlikely D．That's because
