21. —Are there any books about writing on the shelf?
—There are only a few, ________.
A. if there B. if any C. if some D. if ever
22. ________ its low price, the advantage of this car lies in its good quality.
A. According to B. Different from C. Apart from D. Due to
23. _____ the clouds, you would find the airplane in the sky easily.
A. Had it not been for B. If it were not C. If it had not been for D. Were it not for
