Select the most appropriate meaning of the underlined idiom in the sentence.

In spite of the high sounding words, his speech fell flat on the audience.

failed to make an impact

The most appropriate meaning of the underlined idiom in the sentence is >failed to make an impact.<

The idiom "fall flat" means to fail to achieve the desired effect or to be unsuccessful. In the sentence, the author is saying that the speaker's speech, despite its lofty language, did not resonate with the audience and did not have the desired effect.

The other options are not correct.

• Could not be heard clearly: This does not mean to fail to make an impact.
• Appealed to the sentiments of the audience: This does not mean to fail to make an impact.
• Impressed a lot: This does not mean to fail to make an impact.