21.Although it had been______ struggle for him to finish the experiment, he enjoyed the result with________ satisfaction.
A. the, / B. a, / C. a, a D. /, a
22. I shall never forget those years ________ I lived on the farm _______ you visited last week.
A. when; where B. which; which C. when; which D. which; where
23. A large sum of money has been raised the poorly-educated children in the mountainous areas.
A. in return for B. for the benefit of C. in search of D. in memory of
