The audience waited until the curtain had risen and then ________into applause ?

The phrase "burst into applause" is an idiomatic expression that conveys a sudden and enthusiastic reaction from an audience. In this context, "burst" suggests a spontaneous release of emotions, much like a dam breaking, resulting in an overwhelming display of approval. This choice effectively captures the excitement and immediacy of the audience's response once the performance begins.

Choosing "flooded" (Option A) implies an overwhelming quantity but lacks the immediate and explosive nature associated with applause. "Cheered" (Option B), while positive, does not specifically denote the act of clapping and is generally used for vocal expressions of support rather than the physical manifestation of applause. "Started" (Option C) is too vague and passive, lacking the vivid imagery that "burst" provides.

Thus, "burst" is the most fitting choice, as it encapsulates the electrifying moment when the audience transitions from anticipation to enthusiastic engagement, symbolizing the joy and approval that accompanies a successful performance.