1.  ovation

A. outburst
B. bravo
C. applause
D. encore

Answer: Option C

Explanation:

An ovation is prolonged, enthusiastic applause, so applause is necessary to an ovation. An outburst (choice a) may take place during an ovation; "bravo" (choice b) may or may not be uttered; and an encore (choice d) would take place after an ovation.