21. The play had been on for 10 minutes but I was still unable to find a seat_____.
A. to sit B. to sit on C. sit D. sit on
22. _______many times , they succeeded _____ the experiment.
A. Having tried, in doing B. Tried , in doing
C. Having tried, to do D. Tried, to do
23. He fell off his bike and hurt his back. _____, he will have to stay in bed for long .
A. After all B. In any case C. As a result D. In particular
