extemporaneous

他在会议上做了一个即兴演讲，赢得了大家的掌声。

He delivered an ___extemporaneous speech at the meeting, which earned him applause.

那位喜剧演员对飞机餐的即兴调侃让整个俱乐部哄堂大笑。

The comedian's ___extemporaneous riff on airplane food had the entire club roaring.

辩论教练要求每位学生在现场做即兴反驳。

The debate coach required each student to deliver an ___extemporaneous rebuttal on the spot.