21. It is known that water is not _________ endless resource, nor ______ that can be made once more.
A. the; / B. an; one C. an; that D. /; one
22. The president owed his success not to _____ but to self-education and a driving desire for achievement.
A. regulation B. privilege C. arrangement D. procedure
23. Being a green hand in business, she doesn’t know ______ it takes to run a company.
A. what B. that C. how D. which
