6．----Why not take a short break?
-----Didn't we have _______ just now?
A．it B．that C．this D．one
7. Don’t worry too much about __ mistake. They are ___natural part of learning.
A. 不填; a B. the; 不填 C. the; the D. the; an
8． I'm terribly sorry to have kept you waiting so long, but it'll still be some time _______Tony gets back．
A．before B．since C．till D．after
