21. The operation was ______ success, and now the patient is out of ______ danger.
A. /, a B. a, / C. a, the D. /, /
22. At the funny joke, we all ______ laughter.
A. burst out B. broke up C. burst into D. broke out
23. — I have had my computer repaired.
— How much did they ______ you for repairing it?
A. charge B. cost C. spend D. pay
